s 
."Rfc 




Cambridge Agricultural Monographs 



TBasic Slags m' T{pck T^hosp hates 

'By G. S. 'Robertson 







Book JiiL 






CAMBRIDGE AGRICULTURAL MONOGRAPHS 



BASIC SLAGS 

AND 

KOCK PHOSPHATES 






'b ^^ "^ u 



^"'^"'^^ fN OR^.T pp,.„^_ 



DEDICATED TO THE 
MEMORY OF MY BROTHER 

WILLIAM SCOTT ROBERTSON 

LIEUT., ROYAL AIR FORCE 

BORN 1 JUNE, 1898, KILLED IN THE AIR 
OVER THE GERMAN LINES 13 JULY, 1918 

A YOUNG LIFE WHICH GAVE EARLY 

PROMISE OF CONTRIBUTING 

TO THE ADVANCEMENT 

OF SCIENCE 



PREFACE 

By E. J. Russell, D.Sc, F.R.S. 
Director of the Rothamsted Experimental Station 

JLhe utilisation of basic slag in agriculture is an excellent example 
of the help that modern science affords to the working farmer. A 
waste product of steel-making, resulting from a modification by 
Thomas and Gilchrist in 1878 of the Bessemer process, it was at first 
considered worthless and thrown on the refuse heap. The late Prof. 
John Wrightson made field experiments in 1884 and 1885 at Eerryhill 
and at Downton, and showed that the material had noticeable fer- 
tihsing value: this discovery was confirmed and developed by the 
systematic pot experiments of Paul Wagner at Darmstadt, which 
began in 1885 and continued for several years afterwards. Extensive 
field tests were made during the 'nineties by Sir (then Professor) 
J. J. Dobbie and Prof. D. A. Gilchrist at Bangor, and by Prof. W. 
Somerville and later on by Sir T. H. Middleton at Cockle Park, with 
the result that a considerable body of information was accumulated 
as to the effectiveness of basic slag under the various conditions 
obtaining in practice. This has already been summarised by Prof. 
Somerville in the Journal of the Board of Agriculture for 1911, 1918, 
etc. 

Some ten years ago, however, it became evident that the basic 
open hearth process would be a serious competitor with the Bessemer 
process, and chemical examination showed that the slag, though 
correctly described as 'basic slag,' was altogether different from 
the material with which the agriculturist had become famihar. The 
upheaval caused by war and post-war conditions gave an enormous 
impetus to the open hearth process, and it is now extending to so 
many works that before long the older process will probably cease 
to be operated. 

This result is of course distinctly awkward for the agriculturist who 
sees a valuable f ertihser disappearing, and being replaced by one which 
is more costly and at first sight seems to be nothing Hke as good. 

Dr Scott Robertson has the great advantage of being in close 
touch with the steel-making industry, and at the same time of being 
able to carry out agricultural experiments. At the outset of his in- 
vestigations he made a careful selection of the types of slag likely to 



viii PREFACE 

be produced in the future and in 1915 laid out field experiments in 
Essex to compare these newer types with the old familiar Thomas or 
Bessemer slag. These experiments were continued for five years and 
they gave a mass of data so important in character as to deserve wide- 
spread circulation among farmers and agricultural experts. Separate 
publication was therefore advised and the Syndics agreed to its in- 
clusion in the Cambridge Agricultural Monographs. 

Fortunately Dr Scott Robertson had included also some typical 
mineral phosphates in the trials so that valuable information has been 
obtained in regard to a second problem which, while not pressing in 
1915, has grown in importance since and is likely to be serious in the 
future. 

This second problem arises as a direct consequence of the circum- 
stance that basic slag is a by-product only, and not a primary object 
of manufacture. From the steel-makers' point of view it is relatively 
unimportant. Some 4 cwts. only are obtained for each ton of basic 
steel produced, and while the ton of steel has been worth anything 
from £27 in 1920 to £10 in 1921, the 4 cwts. of slag is worth less than 
5s. to the steel-makers and only about 155. even after the slag grinder 
has graded, ground and bagged it. The steel-maker cannot afford to 
alter his processes in any way that would lengthen them or make them 
more costly or hazardous. The agriculturist must therefore take the 
slag as he finds it and cannot expect the consideration that would be 
shown him by the makers, say, of superphosphate, which is a primary 
object of manufacture and not a by-product. The practical result is 
that the composition of basic slag is determined by the conditions 
under which the steel-maker is working, and the total amount pro- 
ducible is regulated by the demand for steel ; neither of which factors 
is in any way within the control of the agriculturist or influenced to 
any appreciable extent by his demands. 

It is important that this distinction between basic slag and other 
fertilisers should be recognised. If the farmers of this country demanded 
double their present supphes of superphosphate, of nitrates, of sul- 
phate of ammonia or of potassic fertiHsers, the manufacturers could 
provide the additional material : if, however, basic slag were desired 
over and above the quantity determined by the demand for steel it 
could not be suppHed except perhaps by importation. 

The position thus created is being explored by the Permanent Com- 
mittee set up by the Ministry of Agriculture to advise on basic slag. 
On the agricultural side there is evidence that the farmers of the 
United Kingdom might with advantage to themselves and the com- 



PREFACE ix 

munity use no less than 890,000 tons per annum, equivalent to 
33,820,000 units of tricalcicphosphate. On the other hand the 1920 
output of British steel yielded about 560,000 tons of slag of 15| per 
cent, or higher content of phosphate, equivalent to 13,400,000 units 
of tricalcicphosphate. There is therefore a considerable gap between 
the farmers' potential demand and the visible supply. The difficult 
problems associated therewith are being fully and sympathetically 
studied by agriculturists and steel-making experts and no doubt 
various solutions will be devised. One obvious possibihty is to use 
ground mineral phosphates to stiffen out the supplies, and here 
Dr Robertson's experiments will prove helpful. 

Dr Robertson has not confined himself to the practical demonstra- 
tion of increased yields: he has gone further and endeavoured to 
ascertain why the increases have been obtained, thus giving the 
monograph a scientific as well as an empirical interest. He examines 
the change in herbage and he shows that the physical properties of 
the soil and the bacterial actions in the soil are much influenced by 
the phosphate in the slag, thus throwing important hght on the view 
now commonly held by experts that poor grassland should not be 
ploughed out till after it has been improved by slag. 

The monograph contains a store of information about the new slags 
and is a model of thorough and systematic investigation. I have 
personally inspected the plots on several occasions and have seen 
much of the experimental work. It deserves close study by all who 
are interested. 

E. J. R. 



January, 1922. 



AUTHOR'S PREFACE 

The main purpose of this book is to put on record the results of the 
field experiments with rock phosphates and open hearth basic slags 
conducted in Essex during the period 1915-20. 

The field trials have been confined to grass land, and the results 
have been measured by increases in the weight of the hay crop, and 
by the improvement in the quality of the crop, as determined by 
botanical analyses. This plan has been adopted for two reasons: first, 
because it is on grass that the primary and secondary actions of 
phosphates are most apparent, and most readily measured ; secondly, 
because on permanent grass, in Essex at any rate, the issue is not 
comphcated by previous appHcations of artificial manures, and it is 
therefore easier to follow out the experiment year by year than under 
arable conditions. 

The objection may be raised that increased weights of hay do not 
give a true test of the improvement which has taken place, and that 
such a test can only be obtained through the medium of the animal. 
While there is much to be said in favour of this contention, it may be 
safely assumed that, when botanical analysis shows the quahty of the 
herbage is similar, the increased weights of hay bear a definite relation- 
ship to the five-weight gains, and do afford a satisfactory method of 
comparing the efficiency of the various phosphates. Moreover, it must 
be remembered that hay is an important crop, and in Essex, as else- 
where, it is the prevalent custom to graze and mow the permanent 
grass in alternate years. 

The Essex results with ground rock phosphates indicate that there 
are soil conditions under which these types of phosphates may be 
expected to give as good and as quick results as the more soluble 
types of phosphatic fertilisers. It is equally clear, however, that under 
other conditions the advantage is decidedly in favour of the more 
soluble types. Experiments in progress in the North of Ireland on 
the turnip crop strikingly bear out this conclusion, and it would seem 
probable that an explanation of the different results secured elsewhere 
might be obtained by means of an examination of soil and chmatic 
conditions. 

I have to acknowledge my indebtedness to Dr E. J. Russell, F.R.S., 
for the great interest he has taken in the work here described. From 



xii AUTHOR'S PREFACE 

the discussions which took place during his annual visits to the various 
experimental centres many helpful suggestions came. 

For the method of estimating nitrates I am indebted to Mr D. J. 
Matthews, till recently of the Rothamsted Experimental Station, and, 
for the nitrate determinations, to my former colleague, Mr R. G. 
Baskett, For the bacterial counts in Tables XLV and XL VI I am 
indebted to Mr James Bryce, B.Sc; for the mechanical analyses in 
Table XXXIX to my former colleague Capt. H, H. Nicholson, M.A. 
(Cantab.) ; for the rainfall data to Mr Carle Salter, the Superintendent 
of the British Rainfall organization, and for the illustrations of Nauru 
and Ocean Islands to Mr A. F. Elhs, the Commissioner for New Zealand 
on the Board of the British Phosphate Commissioners, 

I should also Uke to record my thanks to Messrs B. Smith, N. F. 
Miles, T. Wood, C. L. Petheybridge and A. Freshwater, on whose 
farms the more important of the field trials were laid down, for the 
care they have taken of the plots and for the ready help they have 
given through the whole period of the trials. 

Finally, I have to express my keen appreciation of the kindness of 
the Agricultural Education Committee of the Essex County Council, 
who provided unique f acihties for the work and gave me a free hand 
in the carrying of it out. To the generosity of the members of this 
Committee is due, in no small measure, the opportunity of submitting 
this book to all who are interested in the progress of Agriculture. 

G. S. R. 



The Queen's University of Belfast, 
January, 1922. 



CONTENTS 



INTRODUCTION 

Basic Bessemer Slag 
Basic Open Hearth Slag . 
Rock or Mineral Phosphates 



REVIEW OP PREVIOUS EXPERIMENTS 

Review of Pot Experiments with Insoluble Phosphates 
Review of Field Experiments with Rock Phosphates 



THE ESSEX EXPERIMENTS . . . . . 

Character of the Soil 

Rainfall 

Details of Experiments 

Field Experiments on Boulder Clay Soils . 
Discussion of the Results on the Boulder Clay Soils 
Field Experiments on London Clay Soils 
Discussion of the Results on the London Clay Soils 
Field Experiments on Chalk Soils 
Conclusions drawn from the Field Experiments . 
The Applicability of the Results .... 



AN INVESTIGATION INTO THE REASON WHY BASIC 
PHOSPHATES HAVE CAUSED INCREASED YIELDS 

The Effect of Phosphates on the Botanical Composi 
tion of the herbage 

Discussion of the Results of the Botanical Analysis 

Effect of Phosphates on the Moisture Content and 
Temperature of the Soil 

The Effect of Phosphates on the Texture of the Soil 



PAGE 

1 
2 
4 

8 

10 
10 
11 

18 
18 
20 
21 
22 
29 
30 
42 
43 
45 
48 

49 

49 
59 

63 
73 



xiv CONTENTS 



PAGE 



The Effect of Phosphates on the Accumulation of 

Nitrogen in Grass-land 75 

The Relation of Phosphates to the Accumulation of 

Nitrates in Grass-land . . , . . . 77 

The Influence of Phosphates on Soil Bacteria . . 86 

FACTORS LIMITING THE YIELD OF HAY AND THE ACTION 

OF PHOSPHATES ON HEAVY CLAY SOILS ... 89 

The Effect of Rainfall on the Yield of Hay from the 

Untreated Plots 89 

The Effect of Rainfall on the Yield of Hay from the 

Plots receiving Phosphates 92 

The Second Limiting Manurial Factor .... 95 

THE ACTION OF BASIC SLAG ON THE ACIDITY OF THE 
SOIL AS MEASURED BY THE 'LIME REQUIREMENT' 
AND HYDROGEN ION CONCENTRATES OF THE SOIL 99 

REFERENCES 108 

INDEX ... 110 



PLATES 



I Pouring Slag from Basic Open Hearth Furnace 

Shipping Phosphate from Nauru Island . 
II Ocean Island Phosphate Workings .... 

III Experimental Plots at Martin's Hearne, June 1918 

IV Experimental Plots at Martin's Hearne, June 1918 
V Section of the Soil at Hassobury 

VI Experimental Plots at Horndon, July 1920 . 

VII Samples of Vegetation at Horndon, Aug. 1919 

VIII Samples of Vegetation at Horndon, Aug. 1919 

Photograph of Chalk Pit at Saffron Walden . 



PAGE 

113 
113 
114 
115 
116 
117 
118 
119 
120 
120 



MAP 

Experimental Stations in Essex 



XVI 



INTEODUCTION 

Insoluble phosphates have been apphed to the land in the form of 
bones for a very long time, and until the beginning of the nineteenth 
century it was generally assumed that they owed their value to the 
oil which they contained. Lord Dundonald in his Treatise on the 
Connection of Agriculture with Chemistry, pubhshed in 1795, seems 
to have been one of the first investigators to reahse that the f ertihsing 
value of bones was due to the phosphoric acid which they contained. 
Kirkman writing in 1796 came to the same conclusion, and so did 
de Saussure in 1804. These opinions were accepted and repeated by 
Liebig, who was perhaps largely responsible for the widespread dis- 
semination of this important piece of information. Dundonald in his 
Treatise goes a good deal further than the other investigators, in as 
much as speaking of the phosphate of lime in bones he records: 
"It is a saline compound, very insoluble. There is reason to beheve 
a very considerable proportion of this nearly insoluble salt is contained 
in most fertile soils." It may therefore be said that Dundonald was 
the first investigator to estabhsh the value of insoluble phosphates. 
Towards the end of the eighteenth and the beginning of the nine- 
teenth century the use of insoluble phosphates increased with great 
rapidity throughout Europe, but nowhere more so than in this country. 
By about 1815 the home supply began to prove insufficient to meet 
the large demand, and resort was had to importation from Europe. 
The import of bones grew rapidly, and some idea of the importance 
then attached to the supply of insoluble phosphates may be gained 
from Liebig's passionate outburst : 

England is robbing all other coixtitries of their fertility. Already in her eager- 
ness for bones, she has turned up the battlefields of Leipsic and Waterloo and of 
the Crimea; already from the Catacombs of Sicily she has carried away the 
skeletons of many successive generations. Annually she removes from the 
shores of other countries to her own the manurial eqioivalent of three million 
and a half of men, whom she takes from us the means of supporting, and 
squanders down her sewers to the sea. Like a vampire she hangs on the neck 
of Europe, nay of the whole world, and sucks the heart blood from nations 
without a thought of justice towards them, without a shadow of lasting 
advantage to herself ! 

The discovery of large deposits of rock phosphates in Spain, in 
this country and in other parts of Europe, eased the situation. More- 
over these discoveries came close on the heels of Lawes's patent for 



2 INTRODUCTION 

dissolving bones in sulphuric acid, and at a time when his experiments 
with dissolved bones, and later with dissolved rock phosphates, at 
Rothamsted focussed attention very effectively on the superior value 
of water soluble phosphates. The Rothamsted experiments seem to 
have very rapidly convinced those farmers who followed such develop- 
ments of the superior efficiency of water soluble phosphates, although 
attention was drawn at intervals to experiments which apparently 
showed insoluble phosphates to be as effective as water soluble phos- 
phates. 

BASIC BESSEMER SLAG 

The introduction by Thomas and Gilchrist in 1878 of their process 
for removing phosphorus from the molten pig-iron provided in the 
resulting slag a new source of phosphate for agricultural purposes. 

The presence of phosphorus in steel, except in very small amounts, 
renders the metal brittle and unfit to use for many manufacturing 
purposes. Most of the iron ores in this country are highly phos- 
phatic, and until the coming of the Thomas and Gilchrist process it 
was not possible to remove phosphorus from the pig-iron and so 
produce a good quahty of steel. 

The first step in the manufacture of steel is the conversion of iron- 
ore into pig-iron under the reducing conditions which exist in the 
hearth of the blast furnace. Such reducing conditions are essential 
for the recovery of iron from the ores, but they prevent the oxidation 
of phosphorus, which therefore passes into the pig-iron. 

The conversion of non-phosphatic pig-iron to steel is carried out 
in a Bessemer vessel with a sihceous hning — acid process. If phos- 
phorus is present in the pig-iron phosphoric acid is formed, which, 
being unstable in the presence of an excess of iron, reverts to phos- 
phide of iron, which is not removed in the slag. 

The Thomas and Gilchrist modification of the Bessemer process 
consists in hning the furnace with a basic material instead of a 
siliceous hning, and of adding suitable quantities of hme to the molten 
iron. The phosphoric acid formed combines with the hme producing 
a stable phosphate of calcium, which is removed in the slag which 
floats on top of the molten metal in the converter. 

The process was first tried on a large scale at Messrs Bolckow 
Vaughan and Co.'s Eston Works, in 1879, and a copy of the record 
which illustrates the manufacture of the first Basic Slag is reproduced 
in Table I by the courtesy of Mr Daniel SiUars, chief chemist to 
Messrs Bolckow Vaughan and Co. 



INTRODUCTION 



3 



Table I. Record of the Earliest Manufacture of Basic Slag 

(May, 1879) 



Metal 


Si 


Graphite 


Comb. 
Car. 


Phos. 


Time 
Min, Sec. 


Slags 


Fe 


samples 


SiOa 


CaO 


MgO 


P2O5 




Pig-iron 


2-89 


336 


•06 


1-52 


_ 


_ 


— 


— 


^ 


— 


— 


1 


2-21 


2-64 


•80 


1-51 


3 





— 


— 


^ n 


— 


— 


2 


1-43 


•06 


2-55 


1^51 


6 





— 


— 


tc ao 


— 


— 


3 


•78 


Trace 


2-50 


— 


9 





— 


— 


1" 


— 


— 


4 




Bad sample 
















5 


•13 


Ml 


•53 


1-36 


12 





34-07 


43-53 


9^64 


•60 


5-00 


6 


•10 




Nil 


1-01 


15 





30-40 


41-18 


9^00 


5-02 


6-10 


7 


Trace 






•77 


17 


30 


29-73 


36-58 


8^16 


5-18 


15-90 


8 


Ml 






•41 


18 


30 


23^73 


33-15 


930 


11-10 


10-70 


9 








•12 


19 


30 


20^93 


35^62 


8-50 


10-94 


13-50 


10 








•10 


20 


30 




Bad sample 




Steel 


" 






•18 
Mn. •IS 


21 


10 


2110 


32^84 


9-95 


10-78 


13-60 



In the first blow it will be noted the phosphorus fell from 1-52 % 
in the pig-iron to -18 % in the finished steel. 

When phosphorus has been removed to the required extent the 
converter is tipped forward and the slag allowed to flow over the 
top of the vessel into the slag pot where it is either allowed to cool 
or tipped molten on to the slag heap. 

The production of steel by this process and the consequent accumu- 
lation of phosphatic basic slag increased with great rapidity, and 
attention was turned towards the possibility of using these basic slags 
for fertiHsing purposes. It was at first considered that on account 
of the insolubihty of the phosphates in water the material would 
be of httle value for direct appHcation, Attempts to obtain a suitable 
fertihser by dissolving the slag in acid proved unsuccessful. 

To Wrightson and Munro we owe the discovery in 1885 that if 
basic slag is ground to a fine powder it has a very considerable 
fertihsing value. Their experiments were followed by many others 
including the now classic experiments at Cockle Park, which were 
commenced in 1896 by Professor SomerviUe and subsequently con- 
tinued and developed by Sir T. H. Middleton and Prof. D. A. Gilchrist. 
It is from the Cockle Park experiments that most of our information 
concerning the practical use of basic slag has been derived. These 
experiments continued over a period of 25 years do more than show 
that basic slag has a high fertihsing value. They demonstrate that 
under the conditions at Cockle Park basic slag per unit of phosphoric 



I — 2 



4 INTRODUCTION 

acid is more effective than superphosphate, a result which was sub- 
sequently confirmed by the trials at Sevington, Cransley, Hatly and 
Yeldham(28). At Sevington where the soil is well supphed with calcium 
carbonate (32) the returns for the two types of phosphates are for 
practical purposes identical, there being only a difference of 3 lbs. 
hve weight gain in favour of slag over a period of nine years. 

The superior results from basic slag at the remaining centres is 
probably due to the fact that on 'sour' soils, and on soils where the 
calcium carbonate content is not high, as at Cockle Park (0-59 % 
CaC03),a certain proportion of the phosphoric acid in superphosphate 
is retained by the soil in the form of somewhat insoluble phosphates 
of iron and aluminium. With repeated dressings of superphosphate 
increasingly large proportions of the phosphoric acid revert to such 
insoluble forms. These experiments may therefore be said to have 
estabhshed the fact that insoluble basic phosphates have a distinct 
function in agriculture, and that under certain soil conditions they 
are to be preferred to the water soluble phosphates in superphosphate. 

As a consequence of the Cockle Park experiments basic slag is 
used for the manuring of grass-land almost to the exclusion of other 
types of phosphatic fertihsers. Nor has its use been confined to 
grass-land, where perhaps rapidity of action is not of primary im- 
portance. In the south of Essex, basic slag is used on the arable land 
almost to the exclusion of superphosphate, and many of the most 
progessive farmers have attributed their success to the use of basic 
slag instead of superphosphate on their heavy clay soils, which are 
either devoid of calcium carbonate or have only a very poor supply. 

Some idea of the extent to which basic slag has been appreciated, 
and the lessons which Cockle Park taught assimilated, may be ob- 
tained from the following figures (Table II) showing the production 
and consumption of basic slag during the period 1903-1920. 



BASIC OPEN HEARTH SLAG 

Unfortunately for agriculture important changes in the manu- 
facture of steel have been taking place during the past few years. 
Economic conditions and to a certain extent the working out of the 
higher grade ores have made the basic Bessemer process uneconomical, 
and it has been replaced by the basic open hearth process. In this 
process iron-ore and Hme are charged on to a basic hearth heated 
by producer gas, and the molten metal poured over the heated lime 



INTRODUCTION 5. 

Table II. Prodfctiozst and CoNSFMPTioisr of Basic Slag in the 
United Kingdom. In Metric Tons (thousands) 



Production Imports Exports 



Net 



1903 




148 


9 




9 


? 


1907 




145 


? 




? 


? 


1910 




160 


? 




? 


? 


1913 




404 


51 




169 


286 


1914 




404 


17 




134 


287 


1915 




400 


— 




117 


283 


1916 




360 


— 




39 


321 


1917 




447 


— 




2 


445 


*1917- 


18 


500 


— 




— 


500 


*1918- 


19 


565 


? 




2 


— 


*1919- 


20 


497 


? 




15 


— 


* Seasonal year June 1st to May 31st. 


The 


figxu-es 


i for 1913 to 


1920 


the Ministry of Agriculture 


returns. 











Table III. Basic Bessemer Process 



No. 


Time from 
beginning 


Metal 






Sl 


AG 






Si 


P 


SiOa 


FeO 


MnO 


MgO 


CaO 


P2O5 


1 


Pig-iron 
min. sec. 


1-22 


2-183 


— 


— 


— 


— 


— 


— 


2 


2 46 


0-72 


2-148 


41-15 


2-40 


903 


4-13 


41-27 


0-84 


3 


5 21 


0-15 


2-224 


36-30 


3-97 


1102 


3-39 


39-50 


3-12 


4 


8 5 


0-007 


2157 


34-41 


3-60 


10-72 


3-35 


42-80 


2-99 


5 


10 45 


0-012 


2-096 


31-94 


4-23 


9-94 


4-01 


43-12 


4-02 


6 


13 28 


0-005 


2053 


16-64 


8-42 


8-51 


7-34 


44-37 


7-15 


7 


15 13 


0-008 


1-910 


14-65 


715 


7-39 


6-34 


46-63 


11-60 


8 


19 14 


0-005 


0-230 


12-94 


5-84 


4-25 


6-00 


47-76 


18-83 


9 


19 31 


0-005 


0-139 


12-20 


6-79 


401 


6-26 


48-59 


18-66 


10 


19 49 


0-004 


0-087 


11-71 


7-19 


4-05 


6-38 


48-19 


18-15 


11 


Rail steel 


001 


0145 


12-77 


5-94 


4-80 


6-75 


47-87 


16-92 



Table IV. Z 603. Ordinary Basic Open Hearth Process 







Metals 






Slags 








Time 
p.m. 


















No. 


Car. 


Phos. 


Silica 


Lime 


Total 
iron 


P2O5 


Sol. 
P2O5 


Cit. 
Sol. % 


1 


2.25 


1-77 


-300 


20-30 


33-2 


8^60 


17-08 


15-36 


89-92 


2 


2.40 


1-68 


•327 


19-90 


34-8 


730 


16-87 


14-85 


87-89 


3 


2.55 


1-60 


•35 


18-80 


35-70 


8-40 


17-30 


15-49 


89-53 


4 


3.10 


1-57 


•335 


20-30 


34-90 


6^20 


17-08 


14-08 


82-43 


5 


3.40 


1-48 


•321 


20-20 


3700 


5^60 


15-85 


11-90 


75-70 


6 


4.45 


1-10 


•19 


20-50 


37-70 


5-50 


15-66 


11-78 


75-22 


7 


6.0 


•74 


•083 


15-50 


42-50 


7^20 


15-47 


5-38 


34-77 


8 


7.0 


•63 


•07 


15-10 


40^50 


7^00 


15-75 


4-99 


31^68 


9 


8.0 


•14 


•026 


12-60 


41^80 


11-50 


13-65 


1-79 


1310 


10 


9.0 


-09 


•023 


10-20 


47^80 


14-70 


10-85 


1^66 


15^30 



6 INTRODUCTION 

and ore. The oxygen necessary for the purification of the pig-iron 
is suppHed to the extent of about 70 % by the action of the metalloids 
on the oxide of iron, the balance 30 % coming from the oxidising 
gases of the furnace. In the Bessemer process the oxygen comes 
entirely from the air blast, and the combustion of the phosphorus, 
sihcon, and carbon generates sufficient heat to raise the temperature 
of the steel to the required extent. The slag formed in the basic open 
hearth process is much greater in volume and there is a corresponding 
decrease in phosphoric acid content compared with the basic Bessemer 
process. Tables III and IV show the changes in the composition of 
the slag by the two processes. 

Commenting on Table IV Sillars says : 

The decrease in P2O5 content becomes qtiite sharp after the fourth sample, 
and this, it will be observed, coincides with the commencement of the period 
at which carbon elimination becomes predominant. If high grade slag is 
desired, it is removed at this stage, and after charging fresh lime and oxide 
of iron, the carbon elimination is proceeded with. It will be noticed that the 
phosphorus in the first metal sample is as low as in any of the four immediately- 
following, and it may be asked why the slag coiold not equally well be removed 
at this stage instead of an hour later. The reason is that although the phos- 
phorus is eliminated very rapidly (sometimes it is reduced to 3 % twenty 
minutes after charging), yet it is necessary to delay the removal of the slag 
until all frothing has ceased and \xntil the whole of the hme and ore is dis- 
solved in the bath and the heat is sufficiently high to allow the slag formed 
to flow freely through the tap hole. Unless the slag is removed when it has 
reached the maximum concentration of phosphoric acid, the further additions 
of hme and ore, and the denudation of the fiirnace structure under heat, cause 
an increase in the slag volume which reduces the phosphoric acid content ixntil 
at the termination of the process it will contain from 7 to 10 % only. As the 
content of Hme increases, the slag thickens and reaches a viscosity which slows 
the progress of the 'boil.' This may be corrected by the addition of oxide of 
iron in the form of scale, but if siolphur has to be eliminated from the metal 
it is essential to keep the slag as basic as possible ; the slag is therefore thinned 
by the addition of fluorspar, and it is this addition more than any other con- 
dition which reduces the solubility of the phosphoric acid in 2 % citric acid. 
In Table IV 1 cwt. of fluorspar was added after the sixth sample was drawn, 
and the soluble phosphoric acid fell from 11-78% to 5-38% immediately 
afterwards. 

High grade slag can be obtained by pouring the slag immediately 
before the addition of fluorspar. 

In the basic open hearth process the steel and slag are tipped into 
a ladle — the steel ladle — which is only large enough to hold the steel. 
When the steel ladle is f uU the slag overflows into the slag ladle placed 
immediately under the spout of the steel ladle (Plate I). 

The significance of the change may be better appreciated by a 



INTRODUCTION 7 

consideration of the following figures showing the output in 1920 
of the various grades of basic slag. 



Table V. 



, Gbabe 

1. Over 33 % CajPaOg 

2. 26-33% 

3. 22-26% 

4. 15-22% 

5. 11-15% 

6. Under 11% 

Total all grades 



Production in 1920 
(in tons) 

46,300 
121,400 

90,900 
302,500 
118,000 

22,000 



701,100 



The production of high grade basic slag, even if slag containing 
only 33 % of phosphate is so classed, had fallen by 1920 to less than 
one-tenth of the amount necessary to satisfy the demands of the 
farmer, and it is probable that a comparatively short time will see 
the last of this type of basic slag. 

Of the basic slags forming grades 3, 4, 5 and 6, a large proportion, 
how large it would be difficult to say, are of low citric solubility due 
to the use of fluorspar. It has been shown that the action of fluorspar 
results in the replacement of the calcium silicate in the phosphate 
compound of high soluble slags by calcium fluoride (19) and Bainbridge 
has demonstrated that the resulting slag phosphate consists largely 
of apatite (2). 

There are thus three types of slag available for agricultural purposes : 

1. High grade containing 16-20 % phosphoric acid. Part of this 
supply consists of the rapidly diminishing remnants of the basic 
Bessemer slags and the other part of the slags obtained from the 
basic open hearth process by fractionating before the addition of 
fluorspar. 

2. Open hearth basic slag containing 7 — 14 % phosphoric acid. 

3. Open hearth fluorspar basic slag containing 6 — 12 % of phos- 
phoric acid. 

Numbers 1 and 2 have a citric solubihty of 80-95 % whilst no. 3 
has a citric solubility of from 6-50 %. 

Open hearth fluorspar basic slag is a new material containing 
totally different phosphate compounds to those in nos. 1 and 2. It 
is not the type of basic slag which produced the remarkable results 
at Cockle Park and elsewhere. Its value compared with such slags 
is unknown, and its low solubility suggests that it will prove less 
effective as a fertiliser than the more soluble tjrpes. 



8 INTRODUCTION 

The total production of basic slag, including in that term slags con- 
taining from 1 1 % tricalcium phosphate upwards, amounted to 680,000 
tons in 1920, but, if all slags below 22 % are excluded, to only 258,600. 
Of the totals a very large proportion was fluorspar slag. In 1919 
there was a consumption of at least 560,000 tons and the demand is 
steadily increasing^. Whilst therefore the steel industry may continue 
to be a valuable source of insoluble phosphates for agricultural pur- 
poses, it is becoming increasingly evident that the supply can no 
longer keep pace with the demand and the agriculturist must turn 
to other sources of supply. 



ROCK OR MINERAL PHOSPHATES 

The increasing demand for basic phosphates can most readily be 
met by increasing the output of the apparently inexhaustible stores 
of rock or mineral phosphates and utiHsing these materials for direct 
apphcation. Unfortunately there are no extensive deposits in Great 
Britain^ and there are not many sources of supply within the British 
Empire. (Collins in Chemical Fertilisers gives a map showing the 
distribution of the chief deposits of rock phosphates.) 

Broadly speaking the deposits may be divided into two types — 
the softer and woolher North African phosphate such as Gafsa, 
Egj^tian and Algerian phosphates and the harder North American 
and Island phosphates such as Florida pebble, Carolina, Nauru Island, 
and Ocean Island phosphates. 

The deposits in the majority of cases are close to the surface and 
can be worked, and, in the case of the Island phosphates, transported 
to the shore and shipped at a comparatively low cost. Plates I and II. 

The North African phosphates are more soluble by the Wagner 
test than the harder American phosphates (20). They apparently con- 
tain more calcium carbonate and less calcium fluoride combined in 
the phosphate compound than is the case with the American phos- 
phates (21). It may therefore be just as important to distinguish 
between these two types of rock phosphates as it is to distinguish 
between open hearth fluorspar basic slag and the open hearth basic 
slag produced without the use of fluorspar. 

Rock phosphates have the great advantage of a high phosphatic 
content, ranging in the case of the North African, the Island phos- 

^ Middleton estimates our requirements of basic slag at 891,000 tons per annum. 
^ The deposits of coprolites in Cambridge and Suffolk can no longer be worked 
economically. 



INTRODUCTION 9 

phates and American phosphates from 50-88 % of tricalcium phos- 
phate. Moreover, it has been shown (14) that these phosphates are 
even more soluble in citric acid than the majority of open hearth 
fluorspar basic slags, and that they contain phosphate compounds 
which are in many respects similar to those in open hearth basic 
slags (20). 

It is thus a matter of great urgency to ascertain their precise 
manurial value, as it is no exaggeration to say that the future of 
agriculture and our national prosperity will be largely determined 
by the extent to which suitable phosphates can be supphed at a 
comparatively low cost. 

The problem is a big one, capable of attack from more than one 
point of view. Useful results are Hkely to be secured by investigating 
the effect of chmatic conditions, particularly rainfall, on the avail- 
abihty of the rock phosphates. The question of soil conditions is 
also of great importance in this connection. Rock phosphates for 
example may prove a failure compared with superphosphate on a 
chalky soil under dry conditions, whilst on a sour soil and under a 
more humid cUmate the reverse may well be the case. 



REVIEW OF PREVIOUS EXPERIMENTS 

REVIEW OF POT EXPERIMENTS WITH 
INSOLUBLE PHOSPHATES 

In order to ascertain with any degree of certainty the agricultural 
value of a suggested f ertihser two types of experiments are necessary 
— pot experiments and field trials. Russell (23) discussing the relative 
advantages of field and pot trials points out that as a general rule 
pot experiments are more accurate than field trials. The experimental 
conditions are more under control, and it is therefore possible to 
bring out small differences between materials which it might not be 
possible to secure under the conditions of a field trial. On the other 
hand, the conditions under which pot experiments are conducted are 
so artificial that a positive result is not always paralleled by a positive 
result in the field. Furthermore, though very considerable difference 
in the cropping power of the two materials may be shown by pot 
experiments, it by no means foUows that the differences will be 
equally marked under field conditions. Whilst therefore pot experi- 
ments are of great value as a prehminary method of investigation, 
field experiments are always essential before any deductions can be 
made relative to the economic importance of the factor under investi- 
gation. If they are to be of real value such field experiments must 
be carried out under varying cHmatic and soil conditions and on 
different types of soil, and an attempt be made to interpret the 
results in the light of such conditions. 

Dutton ( 6) during 1912 conducted a series of pot experiments designed 
to ascertain the fertihsing effect of that portion of the phosphoric 
acid in basic slag which is not soluble in citric acid, and came to the 
conclusion that such insoluble phosphate is active enough to feed a^ 
short-hved plant like mustard. 

Bauibridge(2), in a paper on "The Effect of Fluorspar Additions on 
the Phosphates in Basic Slag," describes a series of pot trials with 
barley, and shows that a very insoluble fluorspar slag possessing a 
citric solubility of only 6 %, when contrasted with a slag of 81 % 
solubihty, gives a yield of 61 % compared with the high soluble slag 
yield of 100. These two experiments, although not conclusive, clearly 
indicate that even short-hved crops such as mustard and barley are 
capable of making considerable use of phosphates which are much 



REVIEW OF PREVIOUS EXPERIMENTS 11 

more insoluble than those phosphates which are readily dissolved in 
dilute solutions of citric acid. In view of these results it is reasonable 
to expect that promising returns would be secured from similar trials 
with less resistant materials hke rock phosphates. 

Burhson(3) made an elaborate series of pot experiments with six 
types of rock phosphate, the trials extending over a period of three 
and a half years and embracing the results from 700 pot cultures. 
It is difficult to interpret the exact meaning of these experiments in 
terms of basic slag or superphosphate as neither of these forms of 
phosphatic fertilisers was included in the trials. The results from 
this elaborate series are nevertheless of considerable interest as they 
show that the phosphates in rock phosphates, even of the hard re- 
sistant type like Canadian Apatite, can be assimilated by farm crops 
in sand cultures under greenhouse conditions and in the absence of 
decaying organic matter. Three other conclusions from his work are 
worth noting. Burhson found that the plants could obtain their 
calcium as well as their phosphorus from rock phosphates, and that 
the addition of calcium carbonate to the rock phosphates did not 
produce better results. An attempt was made to ascertain the effect 
of fineness of grinding on the availability of such phosphates, and 
the work shows that better results were secured by grinding beyond 
the '100' grade. Finally the author gives it as his opinion that 
there is no particular relation between the citric acid, soluble phos- 
phoric acid and the availability of rock phosphates to the plant. 

These pot experiments, scanty and incomplete though they may 
be, agree in demonstrating that, under the conditions of the experi- 
ments, the insoluble phosphates in fluorspar basic slag and in rock 
phosphates may have a very considerable agricultural value. 

REVIEW OF FIELD EXPERIMENTS 
WITH ROCK PHOSPHATES 

American Experiments. Although by no means exhaustive, a 
large number of field experiments have been carried out with rock 
phosphates. The subject has perhaps received more attention in 
the United States than elsewhere. There considerable differences 
of opinion exist concerning the fertilising value of raw ground rock 
phosphates or 'floats.' In the States the controversy centres round 
the relative value of ground rock phosphates (floats) and acid phos- 
phate (superphosphate). Most of the American experiments, a detailed 
account of which is given by Hopkins (ii), are confined to this aspect 



12 REVIEW OF PREVIOUS EXPERIMENTS 

of the question. Moreover many of the American State experiments, 
e.g. Maine, Massachusetts, and Rhode Island, compare the two phos- 
phates by applying equal money values, and it is obvious that such 
trials have only a hmited value as far as the apphcation of the results 
to this country is concerned. Moreover, changing economic conditions 
must seriously detract from the value of their apphcation to present 
day American practice. The Ohio, IDinois, and certain of the Massa- 
chusetts experiments compare equivalent quantities of the two forms 
of phosphate, alone and in combination with other manures. These 
experiments have extended through several rotations on duphcate, 
and in some cases triphcate, plots. After an exhaustive review of 
the American experiments up to 1908 Hopkins draws the conclusion 
that rock phosphates are much the more economical type of phos- 
phate to use, and that from the point of view of the permanent f ertihty 
of the soil they are much to be preferred to acid phosphates. 

A later review of the American experiments is given by Waggaman 
and Wagner (31), covering the period up to 1917. These writers give a 
table incorporatiag the results of 232 field experiments. Only 37 of 
these experiments extended over a period of five years or more. Their 
tabulation of these experiments is given in Table VI. 

In explanation of this table they give the following notes: 

Out of the 37 tests given in Table VI, 22 were carried on with a view to 
comparing the relative merits of raw rock and acid phosphates. The conditions 
xm.der which such a comparison was attempted varied greatly, but it may 
be said that in a general way, 13 of these experiments, or 59-1 %, gave crop 
yields as favourable to raw rock as to the more soluble form of phosphoric 
acid. Of the 9 experiments in which raw rock did not compare favourably 
with acid phosphate, 2 were conducted on fields Tinresponsive to phosphate 
treatments and 2 gave results which could be classed as either favourable or 
ixnfavourable, depending on the method of interpretation employed. 

Of the 15 experiments in which no comparison between raw ground rock and 
acid phosphate was attempted, 11, or 73-3 %, gave resvilts strongly indicating 
beneficial effects from the application of the former material, and 2 of the 
remaining 4 experiments were conducted on fields showing little or no response 
to phosphate treatment. 

In 21 experiments the applications of raw rock were relatively light (250 lbs. 
or less per acre), yet 15 of these experiments, or 71-4%, showed distinctly 
favourable increases in yields on the fields treated with this material. 

In 16 experiments where the raw rock applications were more liberal, 13, 
or 81-3 %, resulted favourably to raw rock phosphate, and the remaining 
3 experiments were conducted on soils showing little or no response to phos- 
phate treatment. 

Raw rock phosphate was applied in connection with organic matter in 23 
experiments. Out of this number, 18, or 78-3 %, gave distinctly favourable 
results, and of the 5 remaining experiments 3 were conducted on fields un- 
responsive to other forms of phosphoric acid. 





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14 REVIEW OF PREVIOUS EXPERIMENTS 

In regard to the ciimulative effect of raw ground phosphate rock it may be 
said that in 17 instances (46 % of the entire number of experiments) there 
was evidence of greater availabihty after raw rock had been applied for a 
number of years. In 13 out of the remaining 20 experiments the data are not 
sufficient to give evidence on this point, and in 4 out of the 7 cases where no 
cumulative effect was shown the soils were not responsive to phosphate treat- 
ments. 

The same writers (quoted in tlie Scottish Journal of Agriculture^) 
in a survey of the above experiments conclude that: 

To be efficacious as a fertiliser rock phosphate must be spread evenly over 
the ground as a fine powder. The presence of decomposing organic matter 
increases the efficacy, probably because of the greater bacterial activity pro- 
duced and the higher percentage of carbon dioxide given off. Fineness of 
the powder and the presence of organic matter together prolong the efficacy 
of raw phosphate rock for another year, or even more. On the other hand, 
as the action of superphosphate is more rapid than that of bone powder, 
basic slag and mineral phosphates, it is probably preferable to any other 
phosphatic fertiliser when the aim is to obtain rapid growth of the plants 
cultivated. 

To obtain the best results with powdered rock phosphates, they must be 
appHed in larger quantities than superphosphate. Whether it be best to apply 
rock phosphates in a soluble or insoluble form to produce the most economical 
increase in yield depends on the nature of the soil, the cultural method, the 
price of the phosphates, the duration of the vegetative period, and other local 
factors. It is a question which, to a certain extent, must be solved by each 
farmer individually. 

French Experiments. Grandeau, in the seventh volume of his 
Etudes Agronomique, gives an account of French experiments with 
dissolved and undissolved phosphates on potatoes, wheat and oats. 
The experiments are reviewed by Dyer (8), who records that "contrary 
to generally accepted theories (but conformably with results already 
arrived at in various parts of France) finely powdered mineral phos- 
phates have given yields as large as those of superphosphate — the 
soil being an extremely poor non-calcareous one." 

English Experiments. The earhest experiment on the value of 
rock phosphates was that carried out by Dr Daubeny, on the turnip 
crop, with Spanish phosphorite (5), at the Botanic Gardens at Oxford, 
Very satisfactory returns were obtained from the Spanish phos- 
phorite, which, however, did shghtly better when treated with sul- 
phuric acid. In the same issue of the Journal Sir H. Verney, Bart.(30) 
gives an account of his experiments on barley with this material. 
The experiments were carried out on a heavy sandy loam. In these 
trials Spanish phosphorite gave quite as good results as superphosphate 

1 July 1920, p. 357. 



REVIEW OF PREVIOUS EXPERIMENTS 15 

of Ume, but in this instance also it was not so effective as ' Spanish 
phosphorite and sulphuric acid.' 

Dr Jamiesoni reports two experiments, one conducted in Sussex 
and the other in Aberdeenshire, to test if basic slag really acted as 
effectively as coprohtes, both being used in the same state of division 
and in such quantities as gave equal proportions of phosphate. 

The results were as follows : 





WiSTON 


Glastebberry 




(in Sussex) 


(in Aberdeenshire) 




tons 


cwts. 


tons cwts. 


No phosphate 


25 


17 


6 16 


Coprolite 


28 


11 


29 1 


Slag 


28 


11 


28 11 


Superphosphate 


30 


7 


24 19 



Commenting on these results, Jamieson says: 

The Sussex soil txirned out to be too rich to show distinctly the effect of 
any kind of phosphate, but the Aberdeenshire soil gave conclusive proof. The 
resulting crops of turnips showed that slag and coprolites, in equal state of 
division, are practically identical in their effects on crops. 

Gilchrist records (12) a series of four field trials on three years' ley 
to compare the value of Belgian and Tunisian phosphates with basic 
slags of varying solubihties. Two of the series give results very favour- 
able to Tunisian and Belgian phosphates. The third test, however, 
is not so favourable, and the fourth test had to be abandoned owing 
to the failure of the 'clover take.' In the first of Gilchrist's three 
year tests Tunisian phosphate does not do so well as Belgian, a result 
which Gilchrist attributes to this phosphate not being so rich in Hme. 
It is worthy of note that in the second test Gilchrist gets somewhat 
better results from Belgian phosphate that has been calcined. 

01dershaw(i6), working on a chalky boulder clay soil in Suffolk, 
found that on the hay crop, citric solubihty was of great importance. 
Although low citric soluble slags and a Belgian rock phosphate effected 
a considerable improvement, the high soluble slag gave a much heavier 
hay crop than the rock phosphate or the low soluble slags. In dis- 
cussing his results, Oldershaw makes the following observation, which 
is of considerable importance: "It is worthy of note that had all the 
plots been grazed and the results estimated by inspection only, the 
conclusion might easily have been drawn that Plots B (low soluble 
slag) were almost as good as Plots A (high soluble slag)." 

^ The Farmer's Handbook, p. 46. 



16 REVIEW OF PREVIOUS EXPERIMENTS 

Scottish Experiments. In Bulletin 10 of the North of Scotland 
CoUege of Agriculture details are given of an experiment extending 
over three years, and designed to contrast the effect of superphosphate, 
bone meal, basic slag, and ground Florida phosphate, with and with- 
out farmyard manure, on turnips and the two succeeding crops, barley 
and hay. In the series of plots comparing the four phosphates without 
the addition of farmyard manure, the American rock phosphate gives 
the poorest result. It has approximately the same effect on the barley 
and hay crops as basic slag, but did not prove to be as effective on 
turnips. 

On the other hand, where farmyard manure was given in addition 
to the various phosphates, Florida rock phosphate gave better results 
than any of the other phosphates, and the profit on the rock phos- 
phate plot is more than twice as great as on any of the others. It is 
difficult to draw conclusions concerning the relative efficiency of these 
phosphates when used with farmyard manure. No plot with farmyard 
manure alone was included in the series, and it might well have 
happened that farmyard manure alone would have given as good 
results as farmyard manure plus phosphate. 

Russell (24), in "Notes on Manures" for Jan. 1920, gives a table 
summarising 67 experiments on the turnip crop in Scotland during 
1911-14 with various types of phosphates, including ground mineral 
phosphates. The results show that such phosphates are very nearly 
equivalent to basic slag. It is not clear from this summary, however, 
how much of the gain, amounting to 6 or 7 tons, of the treated plots 
over the untreated is due to the apphcation of phosphoric acid, as 
the treated plots received in addition to the various types of phos- 
phates a dressing of sulphate of ammonia and potash salts. 

Welsh Experiments. Trials with basic slag, Gafsa rock phosphate, 
and superphosphate on Swedes were carried out by the University 
College of North Wales during the three seasons 1913-1915^. Each 
of the phosphates was apphed so as to supply 200 lbs. of phosphoric 
acid per acre. The response to phosphoric acid is decided, and the 
results which are given below are of considerable value. 

AvEBAGE Yield 





Manure 


(3 years) 
tons cwts. 


Plotl 


None 


13 1 


2 


Basic slag 


22 4 


3 


Gafsa 


21 8 


4 


Superphosphate 
1 Bulletin 6. 


22 9 



REVIEW OF PREVIOUS EXPERIMENTS 17 

Commenting on these figures the writer of the Bulletin says : 

Taking the average results of the three years, the crop from this plot (3) 
has been about one ton per acre less than that from the basic slag and super- 
phosphate plots. Under normal conditions it is the cheapest form of phos- 
phatic manure, and, provided that it is finely ground, it may be recommended 
for use in the wet climate of North Wales. It is, however, more likely to prove 
of general value for poor pastures on peat or upland soils, than for swedes on 
ordinary cultivated soils. Even an extra crop of one ton per acre of roots 
would more than cover the difference between the cost of suitable dressings 
of slag and mineral phosphates. 

The above experiments with rock phosphates are by no means 
exhaustive, nor does this summary take account of all the countries 
where experimental work with such phosphates has been conducted. 
The Commonwealth Government of Austraha, for example, has 
offered a prize for the discovery of new phosphate deposits, and an 
account of some preHminary experiments with these materials in 
Western Austraha is given by Paterson(i7). 

The field experiments which have been conducted in this country 
are not convincing, as they have failed to estabhsh the value of rock 
phosphates in the same sense that the Cockle Park and similar experi- 
ments estabhshed the fertihsing value of basic slag. Moreover, no 
explanation has been forthcoming which satisfactorily accounts for 
the favourable results secured at Wiston in Sussex and in Aberdeen- 
shire when compared with slag, and the unfavourable results at 
Saxmundham when compared with the same material. 

It is obvious that data from many more field experiments is neces- 
sary, and if the trials are to be really helpful, each experiment must 
cover a series of years, and an endeavour be made to correlate the 
results with chmatic and soil conditions. 



S.B.S. 



THE ESSEX EXPERIMENTS 

During the winters of 1915, 1916, 1918 and 1919a series of manurial 
experiments under the auspices of the East Anglian Institute of 
Agriculture were laid down on permanent grass-land in Essex with 
the object of ascertaining : 

(1) the relative fertihsing value of the various forms of rock phos- 
phate, the two types of open hearth basic slags, and 

(2) the extent to which the permanent grass on the heavy clay 
soils could be profitably improved. 

The choice of grass as the experimental crop was influenced by the 
fact that it is on grass, whether reserved for hay or pasture, that the 
direct and indirect response to phosphates is most clearly felt. More- 
over, in Essex, out of a total area of 981,000 acres approximately 
300,000 are covered by permanent grass, and as a very large propor- 
tion of this acreage is of the poorest quality, its improvement is of 
considerable economic importance. 

CHARACTER OF THE SOIL 

SHghtly over 600,000 acres, or about two-thirds of the county, is 
covered by soils belonging to the London Clay and Boulder Clay 
formations. 

The London clay beds form part of the Lower Eocene formation, 
and in many parts reach a thickness of over 500 feet. It is a stifiE 
bluish grey or brown clay. Below the London clay Ues a thin bed 
of Thanet sands varying in thickness up to 60 feet. The Thanet sands 
in turn rest upon an eroded surface of chalk. 

The boulder clay soils dominate the northern part of the county, 
and vary considerably in thickness. In the extreme north and north- 
west of the county the boulder clay rests immediately above the 
chalk which comes close to the surface (see Map facing p. 1). South of 
the line Bishop's Stortford — Thaxted — Twinstead, the boulder clay 
lies immediately above the London clay. It nevertheless contains 
a considerable admixture of chalk, sometimes up to 11 %, and it is 
only the extreme southerly and easterly portions that are wholly 
devoid of calcium carbonate. 

As a rule these heavy clay soils are very deficient in phosphoric 
acid, the London clays being also deficient in calcium carbonate. 
Unless the early autumn is favourable great difficulty is experienced 



THE ESSEX EXPERIMENTS 



19 



Table VII. Analysis of the Soils at the Experimental Centre. 
Mechanical Composition 





London Clay 


BouLDEB Clay 


Chalk 




Great Mul- 

graves, 

Horndon- 

on-the-Hill 


•is o a 

"3 "Si =8 

3 ca o 


1 "^ 

m rt rt 


Tysea Hill, 

Stapleford 

Abbotts 


Martin's 

Hearne, 

Stapleford 

Abbotts 


ill 






Fine gravel 


% 

0-31 


% 

0-74 


0-10 


% 
0-66 


% 
0-72 


% 

1-58 


% 

0-81 


% 


Coarse sand 


1-59 


6-27 


19-49 


7-53 


5-15 


26-91 


8-98 


— 


Fine sand 


1509 


26-73 


26-87 


21-58 


24-25 


21-07 


18-34 


— 


Silt 


21-97 


21-12 


14-29 


9-46 


18-51 


13-10 


19-71 


— 


Fine silt 


11-60 


11-50 


15-78 


18-60 


13-90 


9-50 


14-70 


— 


Clay 


29-58 


16-69 


9-78 


18-23 


17-61 


11-53 


20-51 


— 


Loss in solution 


7-50 


7-48 


— 


8-32 


7-61 


5-11 


7-01 


— 


Loss on ignition * 


14-50 


11-82 


11-72 


18-09 


15-29 


12-61 


11-30 


— 




102-14 


102-35 


— 


102-47 


102-63 


101-41 


101-36 


— 



Chemical Analysis 



Loss on ignition 


9-20 


8-24 





12-50 


11-80 


7-23 


8-23 


8-95 


Nitrogen 


0-212 


0-248 


— 


0-406 


0-299 


0-180 


0-208 


0-219 


Iron and 


















aluminium oxide 


14-21 


9-24 


8-35 


11-68 


11-70 


11-63 


11-81 


8-04 


Magnesia MgO . . . 


0-60 


0-77 


0-57 


0-73 


0-73 


0-82 


0-83 


0-60 


Lime CaO 


1-02 


0-94 


0-32 


0-50 


0-49 


0-38 


0-87 


23-14t 


Carbon dioxide 


















CO2 


0-12 


0-17 


0-00 


0-00 


0-00 


000 


0-20 


15-97 


equivalent to 


















Calcium carbonate 


















CaCOg 


0-25 


0-37 


0-00 


0-00 


0-00 


000 


0-45 


36-31 


Potash KgO ... 


0-857 


0-607 


0-508 


0-541 


0-704 


0-435 


0-644 


0-594 


Potash Available 


0-030 


0-0300 


— 


0-0239 


0-0301 


0-0194 


0-0165 


0-0165 


Phosphoric acid 


















PA 


0-078 


0-077 


0084 


0101 


0-089 


0-190 


0-118 


0-210 


Available 


0-0030 


00066 


00043 


00051 


0-0046 


0-0123 


0-0056 


0-0013 


Lime requirement 


















9 ins. sample 


0-00 


0-03 


0-45 


0-29 


0-27 


0-13 


0-00 


0-00 



* Moisture, combined moisture and organic matter. 

f Correction made for moisture content of air dried soil. 



20 THE ESSEX EXPERIMENTS 

in cultivating these soils. After rain the land remains sticky and wet 
for a long time, and it is only too often necessary to postpone the 
sowing of oats and wheat until the spring. During May and June, 
which are dry months in Essex, the soil ' caps ' and cracks, and the 
crops suffer severely from drought. 

An inspection of the grass-land shows that much of it is of the 
poorest quahty. It is but rare that the permanent grass receives 
any manurial treatment, and when reserved for hay it is only in 
favourable years that it passes the ton to the acre level in the western 
and moister part of the county, whilst in the eastern and drier part 
of the coim^ty crops of 7-16 cwts. of hay per acre are the rule, and it 
very frequently happens that the crop is not worth cutting and is 
fed off. 

For the purposes of the experiments soils of the boulder clay and 
London clay formations were selected. A detailed mechanical and 
chemical analysis of these soils is given in Table VII. The soil at 
Horndon is a typical London Clay, that at Latchingdon is better 
described as a London clay-loam, whilst at Lambourne End the 
London Clay is covered by a thick matted turf which extends its 
influence to a depth of several inches. The soils at Tysea HiU and 
Martin's Hearne are typical heavy Boulder Clay soils lying immediately 
on top of the London clay. At Farnham and Hassobury the boulder 
clay rests immediately on top of the chalk, which is about 6-8 feet 
below the surface at Farnham, and 2 feet below the surface at 
Hassobury. 

RAINFALL 

The rainfall records from the various rainfall stations in the county 
show considerable fluctuations. If the county is divided into three 
equal portions by parallel hnes running north and south, the most 
easterly portion might fairly be labelled the driest district in England, 
the average annual rainfaU being approximately 20 inches. (For 
Shoeburjoiess the 35 years' average is 19-28 inches.) The middle 
portion of the county has an average annual rainfaU of 23 to 24 inches, 
the 35 years' average for Chelmsford being 23-02 inches, for Rocking 
23-82, and for Earl's Colne 23-42 inches. The westerly portion of the 
county is considerably wetter, the average annual rainfaU varying 
from 25 to 30 inches, and for most of the stations, for which only 
short records are available, the average is nearer the latter than 
the former figure. In the east of the county the low rainfaU during 
the month of May and the warm drjdng weather which is usuaUy 



THE ESSEX EXPERIMENTS 



21 



experienced dries up the heavy soils, and unless the season is particu- 
larly favourable it is during this month that the growth of the hay 
crop is checked. The western part of the county has the benefit of 
from -6 to -8 inch more rain during this month. Moreover the boulder 
clay, although a heavy soil, is not nearly so heavy as the London 
clay and does not 'cap' and crack so badly as the London clay 
during dry and warm speUs of weather. 

DETAILS OF EXPERIMENTS 

The plots were all one-quarter of an acre in area, with the exception 
of those at Tysea Hill Farm, which were one-fifth of an acre. Three 
types of basic slag have been used. Basic Bessemer slag, basic open 
hearth slag without the addition of fluorspar, and basic open hearth 
slag with the addition of fluorspar. These basic slags have been com- 
pared with the following rock phosphates: Florida pebble, Florida 
soft, Tunisian, Algerian, Gafsa, Egyptian, Cambridge coproHtes, and 
a ferruginous Cleveland phosphate. The composition of these phos- 
phates is given in Table VIII. A more detailed analysis of many of 
these materials has been pubhshed elsewhere (4, 20). At two of the 



Table VIII. 



Partial Analysis of the Phosphates used in- the 
Field Experiments 













Citric soluble 








Total 
phosphoric 
acid P2O5 


Total 

calcium 

oxide CaO 


Silica 
sand 
etc. 






Citric 


Name of phosphate 


Phosphoric 
acidPaOs 


Calcium 
oxide CaO 


solubility 


Basic Bessemer slag 


{I 


% 
17-84 
17-08 


% 
48-82 
45-40 


% 
9-45 

7-48 


% 
16-40 
15-42 


0/ 
/o 


/o 
92-0 
90-3 




1 


11-50 


45-28 


14-94 


10-75 


— 


93-4 


Open hearth high 


.2 


9-69 


46-50 


— 


7-99 


37-13 


82-25 


soluble basic slag 


3 


12-91 


48-12 


12-02 


11-78 


— 


91-20 




u 


9-80 


44-90 


15-39 


8-00 


— 


80-2 




/I 


12-40 


42-40 


15-41 


5-68 


— 


45-0 


Open hearth (fluorspar) ) 2 


11-74 


42-12 


17-35 


2-36 


22-22 


20-1 


basic slag 


3 

4 


9-10 
4-75 


49-31 


— 


2-93 


— 


32-2 




{I 


26-21 


43-51 


6-37 


10-05 


18-54 


38-3 


Gafsa rock phosphate 


26-13 






10-09 


17-86 


38-6 


Egyptian rock phosphate 


26-72 


41-05 


— 


9-28 


15-38 


34-7 


Tunisian „ „ 




24-95 


— 


— 


5-95 


14-14 


23-9 


Algerian „ „ 




29-32 


— 


— 


9-79 


16-82 


33-4 


Florida pebble „ 




33-19 


48-12 


— 


6-06 


9-06 


18-2 


,, soft „ 




25-34 


— 


— 


7-01 


— 


27-7 


Cambridge coprohtes 




26-76 


— 


— 


6-74 


— 


25-2 


Cleveland phosphate 




10-28 


— 


— 


2-01 


— 


19-5 



22 THE ESSEX EXPERIMENTS 

experimental centres, namely Horndon and Hassobury, plots dressed 
with superphosphate, superphosphate and Ume, and hme alone, have 
been included. With one or two exceptions the phosphates were sown 
during the period December to the end of February. Unless speci- 
fically mentioned the initial dressing given was equivalent to 200 lbs. 
of P2O5 per acre, and no further dressings have since been apphed. 
The hay crop was cut during the latter part of June and July, and the 
whole of the crop on each plot weighed immediately before stacking. 
In order to secure uniformity and accuracy the manures were sown, 
the hay crop cut, and weighed under the personal supervision of the 
writer. The necessary labour for weighing the crop on the experi- 
mental plots was brought direct from Chelmsford, and by such means 
interference in the usual routine of the farm during what is a busy 
season was minimised, and it was possible to keep the experiments 
under very effective control. 

FIELD EXPERIMENTS ON BOULDER CLAY SOILS 

Tysea Hill Farm. As far as can be ascertained this field has 
always been under grass, and for at least thirty years prior to the 
laying down of the plots in 1915 had been hayed and grazed in 
alternate years. It is known that prior to 1915 this field had received 
no treatment with artificial manures whatever, although it may, 
many years ago, have received occasional dressings of farmyard 
manure. The soil is sour judged either by the hme requirement figure 
or the Ph. value. The results are given in Table IX and are sum- 
marised in Fig. 1. 

At Tysea HiU there was a rapid and marked response to the various 
phosphates. During the first season the Gafsa rock phosphate plot 
was backward, but during the succeeding years was quite as good 
as any of the other plots on the field, and over the period of the 
experiments the rock phosphate has proved quite as effective as the 
best quahty basic Bessemer slag. 

In the first year of the experiment there was an improvement in 
the quantity of clover present in the herbage on the treated plots, 
but at no period of the experiment was clover present to a very 
marked extent. Although during the last three seasons the untreated 
plots could be distinguished from the treated by the much smaller 
bulk of growth on them, there was never any striking difference 
between the amount of clover present on the untreated and treated 
plots. During the winter the untreated plots could always be dis- 



THE ESSEX EXPERIMENTS 



23 



tinguished by their darker, reddish, unhealthy appearance ; the treated 
plots being able to retain their healthy green colour throughout the 
whole winter. 

Table IX. Weight of Hay at Tysea Hill Farm 
Manures sown: December, 1915 





Manuke 


Citric 
solu- 




Hay (in cwts. per f 


jicre) 




Plot 












Average 
4 years 


J acre 


200 lbs. P2O5 per acre 


bility 

0/ 


1916 


1917 


1918 


1919 


1920 






% 












1916-19 


1 


Basic Bessemer slag . . . 


92-0 


45-5 


28-2 


27-4 


22-4 


40-2 


30-9 


2 


Gafsa rock phosphate. . . 


38-3 


37-1 


30-0 


31-6 


23-2 


41-2 


30-5 


3 


No manure 


— 


31-6 


20-4 


17-7 


11-6 


38-3 


20-3 


4 


Open hearth (fluorspar) 


















basic slag 


45-0 


47-3 


33-5 


29-1 


21-2 


46-4 


32-8 


5 


Open hearth basic slag 


93-4 


46-9 


33-9 


28-7 


21-7 


45-2 


32-8 


6 


Open hearth „ 


82-2 


40-1 


35-9 


29-7 


23-6 


421 


32-3 


7 


No manure 
100 lbs. P2O5 per acre 




34-6 


22-2 


19-8 


14-6 


45-6 


22-8 


8 


Gafsa phosphate 


38-3 


42-6 


33-2 


29-8 


23-5 


48-3 


32-3 


9 


Open hearth basic slag 


















(same as 5) ... 


93-4 


45-2 


29-8 


32-3 


24-3 


44-8 


32-9 


10 


Open hearth (fluorspar) 


















basic slag 


45-0 


50-8 


31-2 


29-5 


21-7 


44-8 


33-3 




Average gain Plots 1, 2, 




0/ 
/o 


°/ 
/o 


% 


% 








4, 5 and 6 over Plot 3 




37-3 


57-8 


66-1 


93-1 








Raiufall, May 1st till 


















harvest (in inches) . . . 




5-94 


5-36 


4-47 


2-87 


9-34 






Plots cut 




July 


July 


July 


July 


Aug. 










19 


12 


6 


9 


23 



























40j- 




r- 
















— 


30- 
























20 - 

10- 




12 3 4 5 6 

Fig. I. Yield of Hay (average of 4 years) from the various Phosphate Plots 
at Tysea Hill. Soil Boulder clay. 
1, Untreated. 2, Gafsa rock phosphate. 3, Basic Bessemer slag. 4, Open hearth (fluor- 
spar) basic slag. 5, Open hearth high sol. basic slag. 6, Open hearth high sol. basic slag. 



24 THE ESSEX EXPERIMENTS 

Equally good results it will be noted have been given by the lighter 
dressing of 100 lbs. of phosphoric acid over a period of five years, 
and it would appear that under the soil and cUmatic conditions of 
this experiment nothing is to be gained by a heavier dressing than 
that represented by 100 lbs. of phosphoric acid per acre. This result 
is interesting, as the soil is as deficient in available phosphoric acid 
as that at Cockle Park, where the heavier dressing of 200 lbs. of 
phosphoric acid per acre proves much superior to the smaller dressing 
of 100 lbs. apphed at more frequent intervals (i3). 

The effectiveness of the various types of phosphates during the 
dry seasons of 1918 and 1919 is of considerable interest. The drier 
the season the greater has been the percentage increase due to 
phosphates. 

Martin's Hearne Farm. The experimental field at this farm 
is only half a mile distant from that at Tysea Hill Farm. The soils 
on the two fields are similar in appearance and in chemical composi- 
tion. The only noteworthy difference shown by the chemical analysis 
is the higher potash content of the soil at Martin's Hearne Farm. As 
far as can be ascertained this meadow has been down to grass for 
at least eighty years before the experiments began. During this 
period no artificial manure of any description has been apphed, but 
the meadow has received during the past twenty years at intervals 
of seven to eight years a dressing of about ten loads of farmyard 
manure per acre. The herbage is of the poorest quahty, weeds such 
as Rumex acetosa, Centaurea nigra, Stellaria media and Ranunculus 
forming a very large proportion of the herbage. 

The results of the experiment at Martin's Hearne are shown in 
Table X and in Fig. 2. The improvement which followed the apphca- 
tion of the various phosphates was even more noticeable than at 
Tysea Hill. During 1917 a thick mat of wild white and red clover 
began to cover the various plots, and during 1918 it was so thick 
on some of the plots as to practically exclude the grasses. The 
appearance of plots 1, 2, 3 and 4 on June 3rd, 1918 is shown in 
Plates III and IV. During the first season (1917) the open hearth 
high soluble basic slag (plot 2) proved more effective than the 
fluorspar slag or any of the rock phosphates. In 1918, however, the 
harvest was late, and the season on the whole moister. In this year 
aU the rock phosphates gave results superior to that of the high 
soluble slag, the superiority of the Gafsa phosphate being quite 
distinctive. In the dry season of 1919, with an early cutting, the 
high soluble slag again proved the most effective, whilst in 1920, 



THE ESSEX EXPERIMENTS 



25 



when the harvest was again late, and the season exceptionally moist, 
the advantage was once more with the rock phosphates. In each of 
the four years the open hearth (fluorspar) basic slag (plot 1) was 
considerably less effective than the other types of phosphate. 

The dense growth of clover which covered the plots in 1918 failed 
to make an appearance in 1919 and all the plots were practically 



Table X. Weight of Hay at Martin's Hearne Farm 
Manures sown: February 20th, 1917 







Citric 




Hay (in cwts. per 


acre) 




Plot 


Mantire 
200 lbs. P2O5 per acre 


solubiHty 
of phos- 














l^acre 












Average 
5 years 






phate (%) 


1917 


1918 


1919 


1920 


1921 


1 


Open hearth (fluorspar) 


















basic slag 


20-1 


230 


28-6 


16-4 


28-4 


9-9 


21-3 


2 


Open hearth basic slag . . . 


91-2 


30-4 


33-4 


27-0 


31-9 


13-4 


27-2 


3 


No manure 


— 


14-3 


23-4 


10-4 


23-0 


9-4 


161 


4 


Gaf sa rock phosphate . . . 


38-6 


23-8 


38-6 


24-8 


35-2 


15-6 


27-6 


5 


Egyptian rock phosphate 


350 


22-8 


35-9 


21-9 


29-0 


10-8 


241 


6 


Algerian „ „ 


35-7 


23-2 


350 


21-0 


34-6 


12-7 


25-3 


A 


Farmyard manure* 


— 


— 


— 


— 


40-3 


17-5 


— 




Rainfall, May 1st till 


















harvest (in inches) ... 


— 


6-27 


11-51 


2-85 


8-37 


2-44 






Plots cut 


— 


July 


Aug. 


July 


Aug. 


July 










23 


10 


9 


9 


5 





* Applied at the rate of 10 loads per acre in the autumn of 1919. 

























4Pn 

30- 

20- 

10- 




1 



6 



Fig. 2. Yield of Hay (average of 4 years) from the various Phosphate Plots 
at Martin's Hearne. Soil Boulder clay. 

1, Untreated. 2, Open hearth (fluorspar) basic slag. 3, Egyptian phosphate. 
4, Algerian phosphate. 6, Gafsa phosphate. 6, Open hearth (high sol.) basic slag. 



26 THE ESSEX EXPERIMENTS 

destitute of clover. During the more favourable season of 1920 the 
clover reappeared towards the middle of June and, although it was 
not so dense as in 1918, it constituted about 30% by weight of the 
crop (Table XXV). Throughout the whole of the winter the untreated 
plot could be picked out a mile away owing to the contrast afforded 
by its dark, reddish, unhealthy colour compared with the healthy 
green of the treated plots. 

As at Tysea HiU, the effectiveness of the various phosphates during 
the dry seasons (1917 and 1919) is again very noticeable, the crop 
on the treated plots being about double that on the untreated. 

Hassobury — Bishop's Stortford. The experimental field at Has- 
sobury has been down to grass for over 90 years. The soil, although 
classified as boulder clay, is of much Hghter texture than the average 
boulder clay soil. At Hassobury it hes immediately above the chalk, 
which is only from two to four feet below the surface. (The photo- 
graph shown in Plate V was taken standing in the ditch at the bottom 
of the field. The chalk can be clearly seen rising to within two to 
three feet from the surface.) The chemical and mechanical composition 
of the soil, as wiU be seen by an examination of the data in Table VII, 
differs considerably from that of the two previous centres. At Hasso- 
bury the soU is comparatively well supphed with phosphoric acid and 
is noticeably poorer in potash. Although so close to the chalk, the 
surface 9 inches of soil is sour, judged either by its lime requirement 
or its Ph. value. 

The pasture is of very poor quahty, the bottom half of the plots 
being covered with a thick almost impenetrable thatch of coarse 
grass. From three-quarters to the whole of Plots 13 to 18 are covered 
with a thick, matted growth, and it is only during favourable seasons, 
and towards the end of the season, that the clover plant seems to be 
able to push its way through in smaU scattered patches consisting 
of a few plants. 

The meadow has been cut for hay practically every year owing 
to the difficulty of getting water to the field, and the aftermath as 
a rule grazed chiefly by horses. 

At this centre a large number of rock phosphates were tried, each 

of them being apphed in two degrees of fineness i. The weights of 

hay on the various plots over a period of three years are given in 

Table XI. 

^ The coarse grade was ground as fine as is usual in the manufacture of super- 
phosphate (90-95% to pass a '60' sieve). The finer grade was obtained by setting 
the Griffin mil l so as to grind as fine as possible. It is not possible to sieve finely 
ground North African phosphates satisfactorily owing to their wooUy nature. 



THE ESSEX EXPERIMENTS 



27 



It is obvious from the results presented in Table XI that some other 
factor than phosphoric acid is hmiting the production of hay on this 
soil. Only in the dry year of 1919 was the response to the various 
types of phosphate in any way marked. Under such conditions no 
useful purpose can be served by discussing the effect of the various 
phosphates. Any differences that may exist must be meaningless 
in view of the smallness of the response and the obvious variations 
in the soil. The soil on Plots 15, 16 and 17, for example, is considerably 
richer in phosphoric acid than the soil on Plots 1, 2 and 3. 



Table XI. Weight of Hay at Hassobury 
Manures sown: January, 1917 







Citric 


Hay (in cwts. per acre) 


Plot 


Manure 


solubility 








J acre 


200 lbs. P2O5 per acre 


of phos- 












phate (%) 


1917 


1918 


1919 


1 


Florida pebble phosphate ( fine) . . . 


19-2 


19-5 


28-0 


15-7 


2 


„ „ „ (coarse) 


18-2 


19-5 


25-0 


15-6 


3 


Algerian phosphate (fine) 


35-7 


18-5 


27-8 


20-8 


4 


„ „ (coarse) 


33-4 


15-7 


27-5 


23-8 


5 


Basic Bessemer slag 


90-3 


13-4 


251 


17-5 


6 


Untreated 


— 


111 


23-4 


10-9 


7 


Gaf sa phosphate (fine) 


41-4 


12-4 


26-8 


19-5 


8 


„ „ (coarse)... 


38-6 


12-1 


25-7 


19-4 


9 


Tunisian „ (fine) 


26-0 


12-2 


29-7* 


16-7 


10 


„ „ (coarse)... 


23-9 


10-7 


33-8t 


14-2 


11 


Egyptian „ (fine) 


370 


10-7 


35-0 


13-3 


12 


„ „ (coarse) 


34-7 


11-0 


34-6 


13-7 


13 


Superphosphate 


— 


14-3 


31-4 


131 


14 


„ (at the rate of 












50 lbs. of P2O5 per acre) 


— 


13-6 


32-8 


10-7 


15 


Superphosphate (200 lbs. P2O5 per 












acre) + 1 ton of ground lime per acre 


— 


11-5 


34-1 


12-1 


16 


Untreated ... 


— 


8-6 


26-2 


7-8 


17 


Open hearth high sol. basic slag... 


91-2 


10-5 


34-3 


9-5 


18 


„ (fiuorspar) basic slag 


20-1 


10-4 


31-6 


8-9 




Rainfall, May 1st tiU harvest (in 












inches) 


— 


4-82 


7-73 


0-58 




Plots cut 


— 


July 7 


Aug. 1 


June 16 



* Plot 9 raked and half cocked. Plots 1-8 lying in the swathe. Hay-making 
interrupted by two days' rain, plots not being weighed tiU four days later. 
t Plots 10-18 inclusive raked and cocked before the rain. 

Farnham Hall. The manures at this centre were not appKed until 
the end of February, 1917. The results for 1917, 1918, 1919 and 1920 
are given in Table XII. 



28 



THE ESSEX EXPERIMENTS 



Table XII. Weight of Hay at Farnham Hall 
Manures sown: February 22nd, 1917 



Plots 


Manube 
200 lbs. P2O5 per acre 


Citric 
solubiUty 
of phos- 
phate (%) 


Hay (in cwts. per acre) 




1917 


1918 


1919 


1920 


1 

2 

3 

4 


Open hearth (fluorspar) 

basic slag 
Open hearth (high soluble) 

basic slag 
Untreated ... 
Gaf sa rock phosphate 


201 
91-2 
38-0 


26-8 

28-2 
24-2 

25-7 


6-3 

6-0 
4-9 
6-6 


7-2 

7-0 
7-9 
8-6 


9-8 

11-5 
111 
111 




Rainfall, May 1st till 

harvest (in inches) 
Plots cut 


= 


3-86 
June 23 


2-97 
June 29 


1-73 
June 26 


2-64 
June 30 



Table XIII. Percentage of GROinsrD Space occupied by the 
Vegetation on the Plots at Farnham Hall: August, 1919 





Farnham (Boulder Clay Soil) 


Type of 
vegetation 


Plotl 

Open hearth 

basic slag 

(solubility, 20%) 


Plot 2 

High citric 

soluble basic slag 

(solubihty,91%) 


Plot 3 

No 
manure 


Plot 4 
Gaf sa rock 
phosphate 


Clovers 
Grasses ... 
Weeds 
Bare space 


27-1 % 
45-0 
16-0 
11-9 


50-2 % 
33-3 
13-5 
30 


16-2 % 
18-4 
250 
40-4 


35-9% 
45-5 
10-6 
8-0 







60 



50 



40 



30 



20 



Ah 



tn 

3 
O 

S-i 



Fig. 3. 
1, Open 



Percentage of Ground Space occupied by the Vegetation at Farnham, 

August, 1919. Soil Boulder clay, 
hearth (fluorspar) basic slag. 2, Open hearth high soluble basic slag. 

3, Untreated. 4, Gafsa rock phosphate. 



THE ESSEX EXPERIMENTS 29 

In spite of the fact that the amount of available phosphoric acid 
in this soil is very low, the response to the various phosphates, judged 
by the yield of hay, is insignificant. The improvement in the three 
treated plots was, however, obvious on walking over them. The clover 
bottom on the untreated plot was very patchy and a considerable 
area of the plot was bare. Plots 1, 2 and 4 were covered with a thick 
bottom of wild white and red clover. In the earher years of the 
experiment Plot 2 had undoubtedly the better bottom, but was 
closely followed by Plot 4, which in 1920 was probably shghtly the 
better plot. Plot 1 — open hearth fluorspar slag — ^was inferior to 
Plot 2 during the first three years of the experiment, but during 
1920 this plot made considerable progress and was quite comparable 
with the other two treated plots. 

During August, 1919, a determination of the ground space occupied 
by the various species on each of the four plots was made and the 
results set out in Table XIII and illustrated in Fig. 3. The high citric 
soluble slag has produced a vast improvement in the herbage, and 
it is quite clear from these comparative results that up tiU then it 
had been the most effective phosphate. 

Although the meadow is an early one, being generally cut during 
the last week in June or the first week in July, still it is somewhat 
surprising that the effect of the phosphate should be confined to 
stimulating the bottom growth and that the improvement so brought 
about should have practically no effect on the jdeld. The results 
seemed to indicate that until some other requirement of the soil is 
satisfied the yield of hay will not be greatly affected by the applica- 
tion of phosphate. 



Discussion of the Results on the Boulder Clay Soils 

At Tysea HiU and Martin's Hearne the two types of soluble slag, 
namely, the basic Bessemer and open hearth basic slag without 
fluorspar, produce in equivalent quantities the same results. The 
open hearth fluorspar basic slag of 45 % citric solubihty gives returns 
strictly comparable with the other two types of slag. The fluorspar 
slag of very low solubihty (20 %) does not do so well and it is distinctly 
inferior at Martin's Hearne (Table X) and Farnham (Table XIII) 
to the more soluble types of slag. The soils at the two centres — 
Martin's Hearne and Tysea Hill — are practically identical, and it 
would be reasonable to expect that the fluorspar slag of 45 % solu- 



30 THE ESSEX EXPERIMENTS 

bility would have done equally well at Martin's Heame and vice versa ; 
that the slag of very low solubUity 20 % would have also given 
inferior results at Tysea Hill. The rock phosphates both at Martin's 
Hearne and Tysea Hill give consistently good results. On this type 
of soil Gafsa rock phosphate may safely be said to be equivalent 
to the better grades of basic slag. Other North African phosphates, 
such as Egyptian and Algerian phosphate, are not far behind Gafsa 
phosphate in this respect. 

Although at Tysea Hill there is apparently no discernible difference 
between the various types of phosphate, yet on a very similar soil 
though shghtly poorer in phosphoric acid, such as that at Martin's 
Heame, a study of the results reveals some important variations in 
their action. During a moist season with a long growing period the 
rock phosphates are on the whole more effective than even the highest 
soluble basic slag. When the season is dry and the growing period 
consequently short the advantage is decidedly with the more highly 
soluble phosphate. 

Under the soil and chmatic conditions existing at Martin's Heame, 
there is over a period of years nothing to choose between the effective- 
ness of rock phosphate and the best grades of basic slag for the im- 
provement of grass-land. The open hearth basic slags of 20 % solubility 
or less, although they give good and profitable results, are clearly less 
effective even in favourable seasons than the high soluble types. 

The lack of response to phosphates at Farnham and Hassobury 
indicates that phosphates are not the most important manurial factor 
on all the boulder clay soils in Essex, and that even where the soil 
is very deficient in available phosphoric acid as at Farnham, a 
deficiency in some other constituent may prevent a profitable response 
to phosphatic manuring. 

FIELD EXPERIMENTS ON LONDON CLAY SOILS 

Horndon-on-the-Hill. A 20 acre meadow which had been laid 
down to grass in or about the year 1890 was selected for these trials. 
The soil is a heavy, impervious London clay, known in Essex as 
three-horse land and always put up in 7 ft. 6 in. stetches so as 
to secure the maximum amount of surface drainage. 

The field, as do aU the fields whether grass or arable on this type 
of soil, hes cold and wet during the autumn and winter, and unless 
there is a good natural slope and good under drainage, water stands 
in the furrows during the greater part of the winter and early spring. 



THE ESSEX EXPERIMENTS 



31 



Table XIV. Weight of Hay at Great Mulgeaves, 

HORNDOlSr-ON-THE-HiLL 





Dressing 200 lbs. PgOg per acre unless otherwise stated 






Citric 








Plnf, 




solubihty 


Hay (in cwts. per acre) 


X X\J\J 


Manure 


of the 








J acre 




phosphate 


















% 


1918* 


1919 


1920 


A 


No manure 





— 




4-5 


B 


Cambridge coprolites 


250 


— 




15-9 


C 


Lime at rate of 1 ton per acre ... 


— 


— 




5-0 


D 


Rough slag (double dressing) 


— 


— 




17-2 


1 


Florida pebble phosphate (fine) ... 


19-2 


14-2 




170 


2 


„ „ „ (coarse) 


18-2 


13-7 




14-7 


3 


Algerian phosphate (fine) 


35-7 


14-7 




21-5 


4 


„ „ (coarse) 


33-4 


14-9 




19-7 


5 


Open hearth basic slag: high sol. 


91-2 


18-8 




23-2 


6 


No manure 


— 


111 


04 


6-4 


7 


Gafsa rock phosphate (coarse) ... 


38-6 


17-8 


8 


22-3 


8 


JJ >> 99 99 """ 


38-6 


18-4 


-s 


22-2 


9 


Tunisian „ (fine) 


26-0 


17-9 


'^ 


23-2 


10 


„ „ (coarse) ... 


23-9 


19-2 


i 


23-8 


11 


Egyptian „ (fine) 


37-0 


23-6 


^ 


23-6 


12 


„ „ (coarse) ... 


34-7 


22-5 


-4^ 


25-1 


13 


Superphosphate (200 lbs. P2O5 per 













acre) 


— 


27-0 


P 


23-0 


14 


Superphosphate (50 lbs. P2O5 per 






TS 






acre) 


— 


25-9 


S 


12-3 


15 


Superphosphate (200 lbs. P2O5 
per acre) — 1 ton of groimd lime 






00 






per acre ... ... 


— 


23-4 


+2 



27-2 


16 


No manure 


— 


15-5 


PM 


6-4 


17 


Open hearth basic slag: high sol. 


91-2 


22-5 




28-8 


18 


„ „ (fluorspar) 


201 


18-8 




16-8 


19 


1 cwt. ferrous sulphate per acre . . . 


— 


13-6 




6-4 


E 


Lime at rate of 1 ton per acre ... 


— 


— 




5-4 


F 


Cambridge coproKtes 


25-0 


— 




151 


G 


Rough slag ... 


— 


— 




10-4 


H 


Cleveland phosphate 


19-5 


— 




190 


K 


No manure ... 


— 


— 




50 


L 


Florida soft phosphate 


27-7 


— 




13-0 




Average gain, Plots 1 to 5 and 7 












to 13 and 15, 17 and 18, over 












plots 6 and 16 


— 


— 


— 


250% 




Rainfall, May 1st tiU harvest (in 












inches) 


— 


2-25 


1-78 t 


5-34 




Date of cutting 


— 


July 8 


— 


Aug. 16 



* Phosphates not apphed till Feb. 27th. 
t Rainfall, May 1st to June 30th. 



32 THE ESSEX EXPERIMENTS 

The summer is equally trying on this type of soil. The dry and hot 
weather which is usually experienced in Essex in June and the latter 
part of May 'caps' or bakes the soil — the soil sets hard and cracks 
and the crops receive a check. It is but seldom that the crop of hay 
exceeds 10 cwts. to the acre, and it is only too frequently left uncut 
altogether. The meadows which have recently been laid down contain 
a smaU reserve of calcium carbonate, a residuum from the heavy 
dressing of lump chalk (40-60 tons per acre) fairly frequently appKed 
up to the eighties or nineties. 

The soil is exceedingly poor in both 'total' and 'available' phos- 
phoric acid, but is well supphed with potash. 

Nineteen quarter-acre plots (1-19) were laid down on this field in 
1918, and the manures sown on February 27th, 1918. Subsequently 
Plots A, B, C, D, E, F, G, H and K were added and sown on February 
3rd, 1919, and finally Plot L was sown during May, 1919. 

The weights of hay on the various plots for the seasons 1918 and 
1920 are given in Table XIV. 

In this experiment an attempt was made to ascertain whether 
better effects could be obtained from rock phosphates by finer grinding. 
With this object in view the Florida pebble, Algerian, Gafsa, Tunisian 
and Egyptian phosphates mentioned in the above tables were specially 
ground under the writer's supervision by Messrs Walter Packard, of 
Ipswich. 

All the phosphates were passed through a Griffin mill. For coarse 
grinding the miU was set to grind for the standard usually adopted 
when the rock phosphates are used for the manufacture of super- 
phosphates (90 % to pass a '60' sieve). In actual fact about 80 % 
of the material wiU pass the ' 100 ' sieve. For fine grinding the mill 
was closed down so that the output per hour was reduced by a half. 
A much finer product was obtained, but it has not been practical, 
owing to the 'wooUy' nature of the rock phosphates, to satisfactorily 
distinguish by means of sieves between the 'fine' and the 'coarse' 
grinding. During 1918 no superiority due to fine grinding was noticed. 

Throughout the whole season of 1920 the writer was able to visit 
this centre at least every week, and a close watch was kept on the 
progress of the various plots. The high soluble slag and the "super- 
phosphate and hme" plots were the first to make a start, followed by 
those plots receiving the finer ground rock phosphates. During the 
whole of May the superiority of the plots receiving the finer ground 
rock phosphates over those receiving the same phosphate only more 
coarsely ground could be distinctly seen. As the season progressed 



THE ESSEX EXPERIMENTS 33 

the distinction became less and less visible, until at the beginning 
of July it was quite impossible to see any difference. 

The high soluble basic slag, Plots 5 and 17, and Plot 15 (super 
and hme) were distinctly ahead during the whole season, but 
the rock phosphate plots gradually lessened the difference as 
the season progressed, although they never actually succeeded in 
catching up. 

The weights of hay for the season of 1920, which was particularly 
favourable to the hay crop, give some indication of the contrast 
which existed between the various phosphate plots and the untreated 
portions. 

It may be of interest to mention that only the plots were cut, and 
no attempt was made to harvest the rest of the field, as the crop was 
not considered to be worth the labour involved in doing so. 

When the wild white clover came into flower the contrast was 
remarkable. Plate VI, showing a general view down Plot K (un- 
treated) and Plot H (Cleveland phosphate), gives some idea of the 
contrast which met the eye. So thick was the crop of wild white 
clover that the farmer decided to seed the plots. 

Plots 1-19 are strictly comparable, having been sown at the same 
time, and a useful comparison of the effectiveness of the various 
phosphates may be made from the respective yields of hay. 

There can be httle doubt that the highest soluble types of open 
hearth basic slag and basic superphosphate have proved the most 
effective phosphates at Horndon. At the same time, however, some 
of the rock phosphates are nearly as effective. From June onwards, 
for example, it was always difficult to say which of the two, Plots 3 
or 5, was the better, although there was no doubt that Plot 3 was 
inferior to Plot 17, which is a duphcate of Plot 5. The hard American 
Florida pebble phosphate is inferior to the softer North African 
phosphates. The inferiority is not only apparent in the weights of 
hay, but is plainly to be seen on walking over the plots, a result 
which agrees with Tacke's conclusion^. 

No gain from fine grinding is apparent in the weights of hay, but 
an earlier start was undoubtedly made by the plots receiving the 
finer ground phosphate, and where a meadow is reserved for grazing it 
is possible that the extra cost of grinding would be weU repaid. 

The open hearth fluorspar slag, after giving promising results 
during the first two years, proved a poor plot in 1920 when compared 
with the high soluble slag, Plot 17. AU the rock phosphate plots, 
1 Inter. Inst, of Agr. Bulletin, September, 1913. 

R.B.S. 3 



34 THE ESSEX EXPERIMENTS 

with the exception of the two receiving Florida pebble, were much 
superior to the open hearth fluorspar basic slag. 

Plots C and E unmistakeably show that Ume without phosphate 
has httle or no effect in improving this type of pasture. 

It is difficult to interpret the results from Plots B, D, F, G, H 
and L in terms of the other plots. They were not sown until 1919, 
and the exceedingly dry season prevented a rapid response. As all 
the plots were grazed throughout this season, these particular plots 
would not receive the same benefit from the grazing as those sown 
the year previously, which, at the beginning of the grazing period, 
were already covered with a thick and close bottom of wild white 
clover. 

During the latter part of May, 1920, Plots B, D, F and H, at first 
backward, made rapid progress, and at harvest time there seemed 
to be more heads of clover on some of these plots than on the majority 
of the others. Plate VI illustrates the appearance of Plot H in 
July, 1920. 

It has been quite obvious during the past two years that the hght 
dressing of superphosphate on Plot 14 has not been effective. The 
improvement was much less than the weight of hay would appear 
to indicate, and during the seasons 1919 and 1920 Plot 14 looked 
very hke an untreated plot. The heavy dressing of superphosphate 
on Plot 13 was much more effective. It was not, however, nearly so 
good as the high soluble slag plots or the " superphosphate and Hme " 
plot. Even on a soil of this character, very deficient in phosphoric 
acid and with a smaU reserve of calcium carbonate, an acid manure 
like superphosphate is not suitable. On Plot 15 the same dressing 
of superphosphate as on Plot 13, namely 200 lbs. P2O5 per acre, plus 
one ton of lime per acre, were sown together. Under such circum- 
stances the reversion of the water soluble phosphate in the super- 
phosphate would be practically instantaneous (22) and the dressing 
would become a basic one comparable to the apphcation of a dressing 
of basic superphosphate. It is of interest to note that Plot 15 gives 
results practically identical with those secured on the plots receiving 
the most soluble type of basic slag. A close observation was kept 
on Plots 15 and 17 throughout the 1920 season, and the only notice- 
able difference was the somewhat earlier start made by Plot 15. The 
difference in this respect was not great, probably not more than 
7 to 10 days, and had visits to the plots been less frequent, might 
have been entirely overlooked. 

During the season of 1919 the long drought lasting from the 



THE ESSEX EXPERIMENTS 



35 



Table XV. Percentage of Ground Space occupied by the 
Vegetation on the Plots at Horndon 



Analysis made : August, 1919 



Plot 


Manube 


Clover 


Grass 


Weeds 


Bare 


J acre 


(Dressing 200 lbs. PgOg per acre) 


% 


% 


% 


space 

% 


C 


Lime alone 


151 


34-6 


30-0 


20-3 


1 


Florida pebble phosphate ... 




46-0 


30-6 


13-3 


101 


3 


Algerian phosphate 




47-4 


301 


7-4 


15-1 


5 


Open hearth high sOl. basic slag 




44-1 


28-6 


13-7 


13-6 


6 


Untreated 




4-2 


14-8 


310 


500 


8 


Gafsa phosphate 




41-3 


32-3 


17-6 


8-8 


9 


Tunisian phosphate ... 




38-5 


36-9 


210 


3-6 


12 


Egyptian „ 




55-5 


410 


0-7 


2-8 


13 


Superphosphate (200 lbs. PgOg per acre) 


23-9 


57-3 


0-7 


18-1 


14 


„ (50 lbs. PgOg per acre) 


18-8 


25-3 


18-8 


37-1 


15 


Superphosphate (as for Plot 13) plus 












1 ton of hme per acre 


60-0 


32-7 


1-4 


5-9 


16 


Untreated 


9-4 


191 


26-0 


45-5 


17 


Open hearth high sol. basic slag (same 












as for Plot 5) 


46-2 


47-2 


1-4 


5-2 


18 


Open hearth (fluorspar) basic slag 












(low soluble) 


43-8 


31-8 


13-3 


IM 


H 


Cleveland phosphate 


431 


33-3 


5-6 


18-0 




Fig. 4. Percentage of Ground Space occupied by the Vegetation at Horndon, 
August, 1919. Soil London clay. 
1, Florida pebble phosphate. 5, Basic slag. 6, No manure. 8, Gafsa phosphate. 
12, Egyptian phosphate. 13, Superphosphate heavy dressing. 14, Superphosphate 
light dressing. 15, Superphosphate and hme. 16, No manure. 17, Basic slag. 18, Open 
hearth fluorspar basic slag. C, Lime. 

3—2 



36 THE ESSEX EXPERIMENTS 

beginning of May until the third week in June made a hay crop out 
of the question, and the plots were therefore grazed by cattle and 
sheep during the remainder of the season. The contrasts between 
several of the plots were, however, so great, that on the suggestion 
of Dr Russell a detailed examination of the ground space covered 
by the various types of vegetation was made on several of the plots, 
using the method recommended by Armstrong (i). 

The results are set out in Table XV, and illustrated in Fig. 4. 
Photographic representations of several of the plots are given in 
Plates VII and VIII. 

The poverty of the untreated plots is difficult to describe, but some 
idea of their unproductiveness is afforded by Table XV, by Fig. 4 
and the lower figure on Plate VI. Amongst the weeds on the un- 
treated plots Hyjpochaeris radicata, Leontodon Mspidus, Ranunculus, 
Prunella vulgaris, Potentilla reptans, Bellis perennis and Plantago 
lanceolata are prominent, and amongst the grasses Holcus lanatus, 
Hordeum pratense, Agrostis vulgaris, Cynosurus cristatus, Lolium 
perenne are also prominent, whilst traces of Dactylis glomerata, 
Phleum pratense and Alopecurus pratensis can be found. 

The transformation which has been brought about by the various 
phosphates is remarkable. Weeds have been largely crowded out and 
the bare space reduced in some cases to vanishing point. On the 
untreated plots the crop was left practically untouched, whilst on 
the plots receiving phosphates the growth had been grazed to the 
ground, and even the clover runners were being eaten by the sheep. 
The contrast remained equally striking right through the whole 
winter. The untreated plot was clearly defined by its dark unhealthy 
appearance and the black heads of the uncropped crested dog's tail. 
On the plots receiving phosphates the mat of wild white clover 
runners remained green throughout the whole winter, and continued 
to afford feed for the stock wintered on the meadow. 

The botanical examination of the flora reveals differences between 
the various phosphates which do not appear so prominently in 
the yields of hay. Whilst the various basic phosphates show but 
small differences, the three plots receiving superphosphate show 
significant contrasts. A very decided improvement has followed the 
heavy dressing of superphosphate, but the small dressing of 50 lbs. 
of P2O5 in the form of superphosphate has had httle effect. The 
addition of Hme at the rate of 1 ton per acre, sown immediately the 
superphosphate had passed through the drill, produces an effect which 
affords a significant contrast with the same dressing of superphosphate 



THE ESSEX EXPERIMENTS 37 

applied alone. Superphosphate alone has had most effect on the 
grasses, whilst superphosphate and Hme together — basic superphos- 
phate — has told mostly on the clovers. 

Armstrong's method of interpreting the results fails to bring out 
any marked distinction between the types of basic phosphates. It 
merely demonstrates that the improvement in quality is approxi- 
mately the same. When the plots are left for hay the differences 
between the phosphates are reflected in the hay yields, but when the 
plots are grazed or when the growth is short inspection of the plots 
gives the impression that there is little to choose between them. 
This difficulty in interpreting results under such conditions is also 
noted by 01dershaw(i6). 

Butterfields, Latchingdon. ThesoilatLatchingdonisnotsoheavy 
as that at Horndon, containing only 16-5 % of clay, against 30 % 
at the latter centre. The soil would be better described as a clay 
loam, resting on a stiff London clay subsoil. In other respects it is 
very similar to Horndon. It is very poor in both total and available 
phosphoric acid, but contains a small reserve of calcium carbonate. 
Eight years before the commencement of the experiments in 1915, 
the experimental field had received a smaU dressing of about 4-5 cwts. 
of basic slag per acre — a dressing which probably accounts for the 
comparatively high proportion of citric soluble phosphoric acid to 
total at this centre (Table VII). 

The meadow, however, was in an exceedingly poor condition when 
the experiments began, and it is evident from the response to the 
various phosphates that the effect of the small dressing applied 
13 years ago was practically exhausted. 

The plots have been cut every year, and the hay crop weighed. 
The figures are set out in Table XVI and the results are shown 
diagrammatically in Fig. 5. 

The figures in Table XVE give some idea of the remarkable response 
to the various phosphates. The improvement in the quality of the 
herbage was equally marked. During the seasons 1916, 1917 and 
1918 the treated plots contained a dense and vigorous growth of 
clover. The open hearth fluorspar slag was quite as effective in this 
respect, during the initial stages of the experiment, as any of the high 
soluble slags, and was in fact superior to either of the two open 
hearth high soluble basic slags on Plots 5 and 6. It has already been 
pointed out that it was not until the second year that the yellow 
suckhng clover and bird's foot trefoil, which formed the natural 
leguminous flora of the untreated plot, were replaced on Plot 2 (Gafsa 



S8 



THE ESSEX EXPERIMENTS 



Table XVI. Weight of Hay at Bftterfields, Latchingdon 
Manures sown: December, 1915 



Plot 


Manure 


Citric 
solubihty 


Hay (in cwts. per acre) 


Average 












J acre 


200 lbs. P2O5 per acre 


of phos- 
phate (%) 


1916 


1917 


1918 


1919 


1920 


5 years 


1 


Basic Bessemer slag 


92-0 


44-4 


24-3 


22-2 


35-9 


20-0 


29-4 


2 


Gafsa rock phosphate . . . 


38-3 


44-2 


19-1 


27-0 


28-3 


17-8* 


27-3 


3 


No manure 


— 


31-4 


14-5 


20-1 


20-6 


161 


20-5 


4 


Open hearth (fluorspar) 


















basic slag 


45-0 


44-7 


23-5 


26-2 


28-7 


21-4 


28-9 


5 


Open hearth basic slag — 


















high citric soluble (1) ... 


93-4 


37-6 


21-9 


32-4 


34-5 


22-6 


28-9 


6 


Open hearth basic slag — 


















high citric soluble (2) ... 


82-2 


40-9 


22-7 


36-3 


35-7 


25-7 


32-3 




Percent, increase of Plots 


















1, 2, 4, 5 and 6 over the 


— 


34-4 


53-8 


43-4 


62-2 


39-2 


— 




unmanured plot (Plot 3) 


















Average rainfall May 1st 


















to June 30th (in inches) 


— 


3-41 


2-32 


2-51 


1-47 


2-28 


— 




Date of cutting 


— 


July 


July 


July 


July 


July 


— 








25 


19 


29 


21 


19 





* During the late winter and early spring of 1919-20 cattle were driven without 
the knowledge of the farmer across a portion of this meadow on their way to a more 
distant pasture. Their track lay right along the length of Plot 2, which they poached 
badly. As a result, although this plot had the best bottom, there was not such a 
vigorous growth as on the other treated plots. 





" 


40 


























_ 


30 


r— 1 1 1 1— 1 


1— j 



a 


























S-i 
ft 


- 


20 


[— 1 






















CO 



- 


1.0 


3 




2 




4 




5 




1 




6 



Fig. 5. Yield of Hay (average of 5 years) for the various Phosphate 

Plots at Butterfields, Latchingdon. Soil London clay. 

3, Untreated. 2, Gafsa rock phosphate. 4, Open hearth (fluorspar) basic slag. 

6, Open hearth (high soluble) basic slag 1. 1, Basic Bessemer slag. 6, Open hearth 

(high soluble) basic slag 2. 



THE ESSEX EXPERIMENTS 



39 



phosphate) by a bottom of wild white clover comparable to that 
on the other plots. During 1919 and 1920, and to a certain extent 
during 1918, it was noticeable that the open hearth fluorspar slag 
on Plot 4 was not doing quite so well as some of the other slags, and 
the weights of hay for these years confirm this opinion. The inferiority 
of both the Gafsa phosphate and the open hearth fluorspar slag plots 
during the dry season of 1919 was also obvious to the eye. 

The behaviour of the clover was the outstanding difference between 
this centre and Horndon. Whereas at Horndon the clover runners 
ramified over the whole of the plots receiving basic phosphates and 
persisted throughout the whole winter, at Latchingdon the clover 
seldom made its appearance before the end of May or the beginning 
of June, and seemed to vanish completely from the plots by the end 



Table XVII. Percentage of the Ground Space occupied by 
THE Vegetation on the Plots at Butterfields, Latchingdon 



Type of 
vegetation 


Plotl 
Basic Bessemer slag 


Plots 
No manure 


Plot 4 

Open hearth 

(fluorspar) basic slag 


Clovers 

Grasses 

Weeds 

Bare space 


18-1% 
56-2 
0-0 
25-7 . 


7-8% 
41-5 

1-6 
49-1 


22-2% 
42-4 
00 
35-4 



of October. During the dry season of 1919 the clover bottom on 
the treated plots, although vastly superior to the unmanured plot, 
was much inferior to what it had been during previous years, or 
during the following year 1920. Not till the rain came at the end of 
June in 1919 did the clover make any real show, and had the plots 
been cut early in July as was intended there would have been Uttle, 
if any, clover in the hay. 

The examination of the flora covering the ground space of Plots 1, 
3 and 4 was made during the third week of September 1919, and the 
results are given in Table XVII. 

As far as the composition of the herbage is concerned, the open 
hearth (fluorspar) basic slag compares very favourably with the basic 
Bessemer slag, and both are greatly superior to the untreated plot. 

Butcher's Farm, Lambourne End. These trials were not com- 
menced until 1919, the manures being sown on January 4th, 1919. 
The writer had been offered a supply of a new 'ferruginous 
phosphate' recently discovered in Cleveland (N.R. of Yorkshire), 



40 



THE ESSEX EXPERIMENTS 



and, through the courtesy of Dr Stead, a small quantity of two open 
hearth slags from the same Steel Works, but of widely different 
solubiHties. 

It was therefore decided to start a new experimental centre in 
order that a fair comparison between the different phosphates might 
be secured. The size of the plots was one-quarter acre, and the usual 
dressing of 200 lbs. P2O5 per acre was given of the various phosphates. 
The plots have received no further treatment. 

Table XVIII. Weight of Hay at Butcher's Farm, 
Lambourne End 





Manures sown: January 4th, 


1919 








Plot 
J acre 


Manure 
200 lbs. P2O5 per acre 


Citric 

solubiHty 

of the phos- 

phate(%) 


Hay (in cwts. per acre) 


1919 


1920 


1921 


Average 
3 years 


A 
1 
2 
3 
4 
5 
6 
7* 

8* 
9 


Cambridge coprolites... 

Open hearth (fluorspar) basic slag ... 

Open hearth basic slag 

No manure 

Egyptian phosphate ... 

Florida pebble phosphate 

Tunisian phosphate ... 

Open hearth (fluorspar) basic slag 

(Wigan) 

Open hearth basic slag (Wigan) 
Cleveland phosphate 


25 
20 
91 

35 
18 
24 

32 

80 
19 


25-0 
26-6 
24-5 
13-2 
18-0 
16-9 
19-0 

16-0 
23-7 
19-9 


32-3 
34-7 
36-2 
21-4 
34-4 
37-8 
38-1 

34-1 
38-0 
38-9 


33-3 

38-5 
310 
18-4 
27-4 
30-5 
34-0 

29-4 
28-5 
34-4 


30-2 
33-3 
30-6 
17-7 
26-6 
28-4 
30-3 

26-5 
30-1 
31-1 




Rainfall, May 1st till harvest (in ins.) 
Date of cutting 


— 


3-08 

July 

17 


5-27 

July 

17 


2-44 

June 

25 





* Plots 7 and 8 = ttto °^ ^^ ^*^^®- 

The condition of the meadow was very different from that of the 
other centres. Instead of a bare open surface as at Horndon, the 
surface was covered with a thick matted turf. Down to a depth of 
about 12 inches the soil was of a fibrous peaty character, and although 
it rested on a London clay sub -soil, the first 9 or 12 inches of soil 
resembled a sour peat soil. Scarcely a trace of leguminous plants 
has been visible on the untreated plot throughout, the hay consisting 
largely of water grasses and the type of weeds characteristic of sour 
soils. 

The soil, as will be seen in Table VII, was very deficient in total 
and available phosphoric acid, it contained no calcium carbonate, 



THE ESSEX EXPERIMENTS 41 

had the high lime requirement of -45 %, and was highly charged 
with organic matter. 

The results are given in Table XVIII. 

Although there are considerable differences between the effect of 
the various phosphates at this centre during the dry season of 1919, 
there are no decided indications that high citric solubihty has been 
of any great importance. The noticeable difference between the returns 
from the two types of open hearth fluorspar basic slag (Plots 1 and 7) 
is somewhat surprising, especially as it is the more soluble of the 
two slags which gives the poorer result. It has, however, been pointed 
out (18) that a modification of the solubihty test, so that 1 gm. instead 
of 5 gms. of the phosphate is used in performing the test, reverses the 
order of solubihty of these two slags. The slag on Plot 1 becomes 
60-6 % soluble whilst that on Plot 7 is only 37-7 % soluble. Difference 
in the nature of the phosphates in the two slags is evidently in this 
case of greater importance than any question of solubihty by the 
Wagner citric acid test. 

During the dry season of 1919 clover was practically absent from 
these plots, and it was not until May of 1920 that it began to force 
its way through the matted turf on the treated plots. In June the 
progress made was remarkable, and by the end of the month the 
treated plots were covered with a thick and vigorous growth of red 
and white clover, which over large areas practically precluded the 
growth of any other type of vegetation (Table XXVIII). The clover 
on Plot 2 (high soluble slag) made better progress than that on Plot 1 
(low soluble slag), and on the whole the high soluble slag was the 
better of the two. The difference was noticeable at the beginning 
of the season, but towards the end it became less and less visible. 
Throughout the whole season Plot 7 (open hearth fluorspar basic 
slag) was much inferior to any of the other plots, and it was rather 
surprising to find it weigh out so heavily. The Cleveland phosphate 
plot was perhaps the best plot on the field, although the superiority 
was not great. The Florida pebble phosphate was slow in making a 
start, but this plot made rapid progress and was ultimately one of 
the best plots on the field. 

In spite of the dry season the 1921 hay crop was quite a heavy 
one, whereas at Martin's Hearne, only a short distance away, the crop 
was practically a failure (Table X). The contrast is probably due to 
the difference in the soils. The heavy soil at Martin's Hearne 'bakes 
and cracks ' during a hot and dry spell of weather, and under such 
circumstances it is likely that the greater part of the heavy fall of 



42 THE ESSEX EXPERIMENTS 

rain on May 26tli (1 inch) was lost by surface drainage. At Lamboume 
End the soil is not heavy and its peaty character no doubt enabled 
it to retain a much greater proportion of the rain which fell on the 26th. 
Over a period of three years the heaviest average crop of hay has 
come from the plot receiving open hearth (fluorspar) basic slag of 
20 % solubihty — the slag which has given comparatively poor results 
at other centres (Martin's Hearne, Table X, and Homdon, Table XIV). 
As if to emphasise the peculiarity the next best return is given by 
the least soluble of the mineral phosphates used in the experiments. 
At Lambourne End citric solubihty is clearly of minor importance 
and the difference in the behaviour of the open hearth (fluorspar) 
basic slag (Plot 1) at this centre and at Martin's Hearne is probably 
accounted for by soil conditions. The Lamboume End soil has a 
much higher hme requirement figure (-45 % compared with -27 % 
at Martin's Hearne) but it is by no means certain that this difference 
alone suffices to explain the results. 

Discussion of the Results on the London Clay Soils 

At aU the centres on the London clay formation there has been 
a marked response to phosphates. The effect of the manures on the 
whole is even more striking than on the boulder clay soils. Differ- 
ences between the relative efficiency of the various phosphates have 
been noticeable. Where the pasture has been down for many years, 
and where as a consequence big stores of organic matter have 
accumulated and the soil has a high 'hme requirement,' and where 
the rainfall is adequate, then rock phosphates prove quite as efficient 
as the best grades of basic slag. Under these conditions open hearth 
(fluorspar) basic slags do not give consistent results. One type of 
open hearth fluorspar slag of very low solubihty proves quite as 
efficient as the highest citric soluble type of slag, whilst another 
open hearth fluorspar slag, apparently more soluble than the former 
one, proves decidedly inferior. 

Where the pasture is comparatively new (30 years or so), where 
the summer rainfall is low, and where a small reserve of calcium 
carbonate still exists in the soil, the best results are secured by the 
highest citric soluble types of basic slag. The improvement effected 
by the best grades of basic slag is, however, closely approximated 
to by the North African rock phosphates. In fact in some years, 
noticeably at Latchingdon, rock phosphates may do considerably 
better than the best grades of basic slag (Table XVI). 



THE ESSEX EXPERIMENTS 43 

The open hearth fluorspar slag of 45 % solubility on the average 
of five years seems to be quite as effective at Latchingdon as the 
most soluble types of slag, although it seems to be somewhat less 
effective during the fourth and fifth years of the experiment. 

The low soluble open hearth fluorspar slag (20% soluble), although 
it gave promise of good results at Horndon during the first two 
seasons, fell far behind during the favourable season of 1920, and 
proved to be inferior to the more insoluble types of rock phosphate. 
This slag also proved less effective on the boulder clay soil at Martin's 
Hearne (Table X). It is not suggested that this slag is of little value. 
On the contrary the improvement effected is really very marked in 
aU cases, and only suffers by comparison with the other phosphates. 

FIELD EXPERIMENTS ON CHALK SOILS 

Wendens, Saffron Walden. The lower photograph on Plate VII 
illustrates the character of the soil at this centre. The chalk is covered 
by a thin layer of boulder clay soil, mixed with a large proportion 
of chalk. The first nine inches of soil at Wendens contains upwards 
of 36 % of chalk. It is naturally comparatively rich in phosphates, 
and although the available phosphoric acid figure is low (Table VII) 
this is no doubt due to the calcium carbonate neutrahsing the citric 
acid. This type of soil dries out quickly. It therefore makes an early 
start in the spring, and the meadow hay is always ready to cut during 
the second or third week of June. In this respect, therefore, the 
conditions are somewhat different from those at the other experi- 
mental centres, which are known as late meadows and which are 
not harvested before the second week of July. 

The experimental field at Wendens was allowed to faU out of 
cultivation about 25 years ago. No seeds of any description were 
sown, and the meadow is therefore a natural one. The general practice 
has been to cut the field every year for hay, and to fold the aftermath 
with sheep. The pasture is of a much superior type to that on any 
of the other experimental centres. The same phosphates were used 
at this centre as at Latchingdon and Tysea Hill Farm. The weights 
of hay for the five years 1916-1920 are given in Table XIX, and 
are represented diagrammatically in Fig. 6. 

The results at this centre are of considerable interest because they 
show that even on an early meadow the more insoluble types of 
phosphate, such as those represented by rock phosphates and the 
better types of open hearth (fluorspar) basic slag, are capable of 



44 



THE ESSEX EXPERIMENTS 



Table XIX. Weight of Hay at Wendens, Sapfron Walden 
Manures sown: January, 1916 



Plot 


Manure 


Citric 
solubility 


Hay (in cwts. per acre 
















J acre 


200 lbs. P2O5 per acre 


of phos- 
phate (%) 


1916 


1917 


1918 


1919 


1920 


Average 
5 years 


1 


Basic Bessemer slag ... 


92-0 


68-5 


30-4 


42-6 


23-4 


39-8 


40-9 


2 


Gaf sa rock phosphate . . . 


38-3 


62-8 


31-5 


39-7 


20-7 


36-2 


38-1 


3 


No maniire 


— 


51-2 


25-4 


33-4 


14-3 


28-0 


30-4 


4 


Open hearth (fluorspar) 


















basic slag 


45-0 


64-9 


35-1 


42-3 


17-7 


39-7 


39-9 


5 


Open hearth basic slag 
(high soluble), (1) ... 


93-4 


54-8 


34-4 


35-7 


15-9 


36-7 


35-5 


6 


Open hearth basic slag 


















(high soluble), (2) ... 


82-2 


60-3 


40-4 


42-6 


17-8 


34-1 


39-2 




Average increase of 
Plots 1, 2, 4, 5 and 6 


















over Plot 3 


— 


21-6 


36-0 


21-6 


33-5 


32-2 


— 




Rainfall, May 1st till 


















harvest (in inches) . . . 


— 


4-00 


4-00* 


2-44 


0-63 


2-42 






Plots cut 




June 


June 


June 


June 


June 










17 


16 


29 


19 


22 





* 2-3 inches feU on May 20th. 



50[-| 



40 



30 



20 



10 



fii 



Fig. 6. Yield of Hay (average of 5 years) for the various 

Phosphate Plots at Wendens, Saffron Walden. Soil Chalk. 

3, Untreated. 2, Gafsa rock phosphate. 6, Open hearth (high soluble) basic slag. 

4, Open hearth (high soluble) basic slag. 1, Basic Bessemer slag. 



THE ESSEX EXPERIMENTS 45 

giving returns comparable to those obtained by the use of the old 
basic Bessemer slag. The explanation probably rests on the fact that 
rainfall is the most important limiting factor on this type of soil. (It 
wiU be observed that the hay crop varies from 14-3 cwts. per acre 
in the dry season of 1919 to 51'2 cwts. during the favourable season 
of 1916.) Shortage of phosphate is possibly the second Umiting factor, 
and the original dressing appUed is more than is essential. 

Conclusions drawn from the Field Experiments 

With two exceptions the field experiments show a marked response 
to phosphates. The failure at Hassobury is probably partly due to 
the fact that the soil is comparatively rich in phosphoric acid, and 
partly to the fact that it is very much poorer in potash than the soil 
at those centres where a response to phosphates was secured. The 
failure at Farnham is not due to the soil being well suppHed in 
phosphoric acid, but to a deficiency in some other factor. 

If the centres where a definite response has been secured are con- 
sidered, it is quite apparent that good results can be expected on 
both the London clay and boulder clay soils from the various types 
of rock phosphates, and that, considered over a period of four or 
five years, it is reasonable to expect these phosphates to give results 
approximately equivalent to those secured from the high citric soluble 
types of basic slag. Seasonal differences have, however, been apparent 
which suggest that the rock phosphates require a considerably higher 
rainfaU to produce the maximum effect than is the case with the high 
soluble slags. These differences are clearly apparent at Martin's 
Hearne, Latchingdon and Lambourne End. The seasons 1917 and 

1919 were dry, or comparatively so, whilst those of 1916, 1918, and 

1920 were moist. If the results for the two dry years on the high 
soluble slag plot and the Gafsa rock phosphate plot, and the corre- 
sponding results from the moist season, are compared as is done in 
Table XX the influence of the season on the availabihty of the rock 
phosphates wiU be seen to be very pronounced. 

During dry seasons high soluble basic slag gives considerably better 
results both at Martin's Hearne and at Latchingdon. Latchingdon 
is in the eastern and drier portion of the county, whilst Martin's 
Hearne is in the western and moister section, and it is of interest to 
note that, as might be expected, the advantage of the high soluble 
slag over the Gafsa rock phosphate is greater at Latchingdon than 
at Martin's Hearne. 



46 



THE ESSEX EXPERIMENTS 



The relative position of the two types of phosphate during the 
wet seasons is curious. At Martin's Hearne the rock phosphate has 
a decided advantage. It also does a trifle better at Latchingdon, but 
the advantage is so small as to be well within the limits of experi- 
mental error. 

The results at Lamboume End (Table XVIII) for the dry season 
of 1919 and the moist season of 1920 fully bear out the results recorded 
above. 

The soil at Martin's Hearne has considerably more organic matter 
in it than the soil at Latchingdon. Moreover it is a ' sour ' soil, with 
a Kme requirement of -27 %, whilst the soil at Latchingdon has a 

Table XX. Effect of Rainfall on the Availability 
OF Rock Phosphates 



Centre 



AvEBAGE Weight of Hay 
(in cwts. per acre) 



Gafsa 
phosphate 



High 

soluble 

basic slag 



in- 
crease due 
to solubility 



Average 
rainfall 
May 1st 
tiU harvest 
(inches) 



Martin's Hearne 
Latchingdon 

Martin's Hearne 
Latchingdon 



Dry seasons, 1917 and 1919. 

. I 24-3 I 28-7 I 4-4 I 

. I 23-7 I 30-1 1 6-4 I 

Moist seasons, 1916, 1918 and 1920. 



Lime 
require- 
ment 
of soil 

/o 



36-9 
29-7 



32-6 

28-9 



-4-3 
-0-8 



4-06 
3-74 



8-92 
609 



•27 
•03 



•27 
•03 



small reserve of calcium carbonate and has only a neghgible Kme 
requirement. It would seem therefore that, on ' sour ' soils well sup- 
phed with organic matter and situated in districts with a moderately 
high rainfaU, rock phosphates may give even superior results to 
those secured from basic slag. 

In Table XXI the average returns from rock phosphates and basic 
Bessemer slag on the ' sour ' soils are contrasted with the corresponding 
results from those centres where the soil is 'sweet,' that is, has a 
reserve of calcium carbonate and no Hme requirement. 

The differences, although small, are probably real. The figures for 
Martin's Hearne, for example, are compiled from four rock phosphate 
plots over a period of four years, for Lambourne End from five rock 
phosphate plots over a period of two years, and two high soluble 
slags over a similar period. Those for Latchingdon and Saffron Walden 
represent one rock phosphate plot and one basic Bessemer slag plot 



THE ESSEX EXPERIMENTS 



47 



over a period of five years, whilst at Horndon the results are made 
up from ten rock phosphate plots and two open hearth high soluble 
basic slag plots for a period of two years. 

Table XXL Comparison of Results on Sour and Sweet Soils 



Centre 


Lime 
require- 
ment of 
soil 

% 


Ph. 

value 

of 

soil 


Eock 
phos- 
phate. 
Average 
cwts. per 
acre 


Basic 
Bessemer 

slag. 
Average 
cwts. per 

acre 


Sour soils : 










Tysea Hill ... 
Martin's Hearne 
Lambourne End 


0-29 
0-27 
0-45 


5-7 
6-1 


30-5 

28-8 
28-0 


30-9 

30-7* 
30-6* 


Average 


— 


... 


29-1 


30-7 


Sweet soils : 










Latchingdon ... 
Saffron Walden 
Horndon 


003 
0-00 
0-00 


7-8 

7-7 


27-3 
38-1 
19-5 


29-4 
40-9 
23-4* 


Average 


— 




28-3 


31-2 



* Open hearth high soluble basic slags. 

The results shown in Table XXI, although they do not agree with 
those secured by Pfeiffer^, yet demonstrate that rock phosphates 
compare more favourably with basic slag on 'sour' soils than on 
chalky soils. 

Had the seasons of 1917 and 1919 been as favourable as those of 
1916, 1918 and 1920, it is probable that the contrast would have been 
more marked. 

Open hearth fluorspar basic slags are very uncertain in their action. 
The improvement effected by their apphcations has in every instance 
been considerable, but the lower soluble types have undoubtedly 
proved to be less effective than either the high soluble slags or the rock 
phosphates. At only one experimental centre (Lambourne End) has 
the open hearth fluorspar slag of 20 % solubiHty given results com- 
parable with the high soluble slag. The open hearth slag of 45 % 
solubihty has proved quite as effective as the best grades of slag and 
rock phosphates. On the other hand, an open hearth slag of 30 % 
solubihty has given at Lambourne End inferior results to a similar 
slag of 20 % solubihty. The relation of citric solubihty to the value 
of the phosphate has been discussed elsewhere (18), 

^ PfeifEer is quoted in the Inter. Inst, of Agric. Bulletin, September, 1913, p. 1316, 
as follows: "on sour soils and on peat moss soils crude earthy phosphates (Algerian, 
Gafsa, etc.) do better than basic slag." 



48 THE ESSEX EXPERIMENTS 

The Applicability of the Results 

It must be borne in mind when considering these experiments that 
the rainfall conditions in Essex are not favourable to insoluble phos- 
phate. In view, therefore, of the fact that rock phosphates have 
proved, even under unfavourable conditions, to be but little inferior 
to the best grades of basic slag, it seems fair to conclude that the 
results detailed here are apphcable to the heavy clay pasture and 
meadow land which cover large areas in this country. 

The impression gained from close observation, of the various experi- 
ments over a period of five years leads to the conclusion that rock 
phosphates are slower in their action during the spring and early 
summer, but if the crop continues to grow until the latter end of 
July this disadvantage disappears. If, however, the harvest is early, 
the advantage is with the higher soluble phosphate. It is probable, 
therefore, that for root crops where the growing period continues 
well into the autumn, rock phosphates wiU prove almost as effective 
as the best grades of basic slag^, and in the northern and western 
parts of the country, where the corn harvest is late and the rainfall 
high, rock phosphates of the North African type may reasonably be 
expected to prove a suitable substitute for the high grade basic slags 
of the past. 

1 Journal Department of Agric. and Tech. Institute for Ireland, Jan. 1917. 



AN INVESTIGATION INTO THE REASON 

WHY BASIC PHOSPHATES HAVE CAUSED 

INCREASED YIELDS 

THE EFFECT OF PHOSPHATES ON THE BOTANICAL 
COMPOSITION OF THE HERBAGE 

JVliDDLETON(i5) in his paper on "The Improvement of Poor Pastures " 
puts to himself the following question: "Why do phosphates produce 
so rapid an increase?" He states that a study of tables recording 
live weight gains or yields of hay will not supply the answer, but 
"that the pastures themselves when closely examined clearly explain 
the action of the manures." He attributes the results to: (1) the 
very rapid increase in the leguminous herbage which takes place; 

(2) a rapid improvement in the quahty of the surface soil; and 

(3) the accumulation of atmospheric nitrogen fixed by the nodule 
organisms. He gives it as his opinion, formed from his careful inspec- 
tion of the various experiments, that phosphates have Httle or no 
direct action on the grasses, and that it is the hme in the basic slag 
acting on the nitrogen accumulated by the nodule organisms which 
brings about the improvement in the grasses. This improvement 
does not take place until the clover has been well estabhshed. Finally 
Middleton concludes that it is impossible to obtain a purely legu- 
minous herbage, that clovers wiU partly and sometimes almost com- 
pletely disappear in three or four years as a consequence of the 
competition of the grasses encouraged by the nitrogen accumulated 
in the soil by the clover nodule organisms. Gilchrist comes to very 
much the same conclusions in his reports on the Tree Field results. 

In order to obtain more detailed information concerning the effect 
of phosphates on the composition of the hay crops in Essex, botanical 
analyses of the hay on the plots at several centres were made during 
the season of 1919, the samples being taken the same day as the hay 
was cut. 

Martin's Hearne and Tysea Hill. The results from the experi- 
mental centres at Martin's Hearne and Tysea Hill are set out in 
Tables XXII and XXIII. 



50 



EFFECT OF PHOSPHATES 



Several points of interest are brought out by these two tables. The 
luxurious bottom of red and white clover which covered the treated 
plots at Martin's Hearne in 1918 (see Plates III and IV) had aU but 
vanished during the 1919 season, and Leguminosae formed only a 
fraction of a per cent, of the hay crop at both the above centres. 
Nevertheless, the contrast in the botanical analysis of the treated 

Table XXII. Botanical Composition, by Weight, of the Hay at 
Martin's Hearne Farm 

Soil: Boulder clay. Manures sown: Feb. 28th, 1917. 
Sample taken: July 9th, 1919 



Species 


Ploti 

Open 

hearth 

(fluorspar) 

basic slag 

% 


Plot 2 

Open 

hearth 

high 

soluble 

basic slag 

% 


Plots 

No 
manure 

% 


Plot 4 

Gafsa 

rock 

phosphate 

% 


Plots 
Egyptian 

rock 

phosphate 

% 


Plot 6 
Algerian 

rock 
phosphate 


Clovers 

Grasses 

Weeds 


trace 
85-2 
14-8 


trace 
88-1 
11-9 


trace 
58-5 
41-5 


trace 
82-6 
17-4 


trace 

96-7 

3-3 


trace 

95-8 

4-2 

















Composition of the grasses by 


weight 






Lolium perenne ... 


9-9 


22-0 


6-8 


26-9 


19-8 


17-0 


Phleum pratense ... 


6-0 


7-7 


2-8 


4-5 


5-7 


1-9 


Cynosurus cristatus 


20-6 


14-7 


10-8 


25-2 


28-7 


10-6 


Poatrivialis 


1-3 


120 


0-6 


10-9 


7-3 


9-5 


Avena flavescens 


1-3 


1-4 


0-6 


1-0 


1-3 


0-6 


Festuca ovina 


— 


0-9 


— 








— 


Holcus lanatvs ... 


32-5 


29-7 


44-3 


18-0 


17-0 


29-0 


Agrostis alba 


0-7 


2-6 


6-8 


4-5 


4-8 


11-2 


Anthoxanthum odoratum 


27-7 


9-0 


27-3 


9-0 


15-4 


20-2 




100-0 


100-0 


100-0 


100-0 


1000 


100-0 


Superior grasses 


391 


58-7 


21-6 


68-5 


62-8 


39-6 


Inferior grasses ... 


60-9 


41-3 


78-4 


31-5 


37-2 


60-4 



and untreated plots is very striking indeed. The hay on the untreated 
plots at both centres consists largely of weeds, and poor undesirable 
grasses such as Holcus lanatus, Agrostis alba and Anthoxanthum 
odoratum. The apphcation of phosphates has either directly or in- 
directly considerably affected the botanical composition of the grasses. 
The better types of grasses such as Lolium perenne, Phleum pratense, 
Cynosurus cristatus and Poa trivialis show a general increase on aU 
the treated plots. With the exception of the open hearth (fluorspar) 
basic slag at Martin's Hearne, all the phosphates seem to be equally 
effective in bringing about the change. Although the clovers have 



ON BOTANICAL COMPOSITION OF HERBAGE 



51 



Table XXIII. Botanical Composition, by Weight, op the Hay 
AT Tysea Hill Farm 

Soil: Boulder clay. Manures sown: December, 1915. 
Samples taken : July 9th, 1919 



Species 


Plotl 

Basic 

Bessemer 

slag 

% 


Plot 2 
Gafsa 
rock 
phos- 
phate 
% 


Plots 

Un- 
treated 
% 


Plot 4 
Open 
hearth 
(fluor- 
spar) 
basic slag 
% 


Plot 5 
Open 
hearth 
high sol- 
uble basic 
slag 1 
% 


Plot 6 
Open 
hearth 
high sol- 
uble basic 
slag 2 


Plot? 
Un- 
treated 
% 


Clovers 

Grasses 

Weeds ... 


trace 
89-1 
10-9 


trace 

90-5 

9-5 


trace 
66-7 
33-3 


trace 

93-7 

6-3 


trace 

91-0 

9-0 


trace 

94-5 

5-5 


trace 
71-8 
28-2 




100-0 


1000 


100-0 


1000 


1000 


100-0 


100-0 



















Composition of the grasses by weight 



LoUum perenne 


31-1 


22-5 


15-3 


21-2 


20-6 


21-5 


5-4 


Phleum pratense 


2-0 


1-3 


— 


50 


4-1 


4-6 


— 


Cynoswrus cristatus ... 


18-4 


19-5 


130 


22-4 


18-5 


16-0 


16-0 


Avena flavescens 


2-4 


4-2 


— 


1-0 


1-2 


0-9 


2-3 


Hordeum pratense 


2-4 


1-3 


3-9 


1-2 


2-5 


5-0 


5-9 


Holcus lanatus 


27-6 


27-4 


41-5 


24-8 


27-7 


19-6 


250 


Agrostis alba 


5-6 


14-3 


140 


12-2 


14-4 


21-4 


14-4 


Anthoxanthum odoratum 


10-5 


9-5 


12-3 


12-2 


110 


11-0 


31-0 




1000 


1000 


1000 


1000 


1000 


100-0 


100-0 


Superior grasses 


53-9 


47-5 


28-3 


49-6 


44-4 


43-0 


23-7 


Inferior grasses 


46-1 


52-5 


71-7 


50-4 


55-6 


570 


76-3 




Fig. 7. Botanical composition of the Hay, by weight, at Martin's Hearne. 
Season, 1919. Soil Boulder clay. 

1, Open hearth (fluorspar) basic slag. 2, Open hearth (high soluble) basic slag. 

3, Untreated. 4, Gafsa rock phosphate. 5, Egyptian rock phosphate. 

6, Algerian rock phosphate. 

4—2 



52 



EFFECT OF PHOSPHATES 



disappeared, the improvement in the grasses has succeeded in reducing 
the amount of weeds to about one-third of that present in the hay 
from the untreated plots. The main points of difference are illustrated 
in Figs. 7 and 8. 



1-170 



60 



O 



W _ 



Ph 





Good Gross 
Inferior Grass 
Weeds 


'1^^^/f1 


mk> 



50 



40 



30 



20 



-10 




1 

r 










Fig. 8. Botanical composition of the Hay, by weight, at Tysea Hill. 
Season, 1919. Soil Boulder clay. 

1, Basic Bessemer slag. 2, Gafsa rock phosphate. 3, Untreated. 4, Open 
hearth (fluorspar) basic slag. 5, Open hearth (high soluble) basic slag 1. 
6. Open hearth (high soluble) basic slag 2. 



Table XXIV. Peecentage of Ground space occupied by the 
Vegetation at Tysea Hill and Martin's Hearne 





Tysea Hill 


Maktin's Heabne 




Plot 1 Plot 3 
Basic slag Untreated 


Plot 2 
Basic slag 


Plots 

Untreated 


Clovers 

Grasses 

Weeds 

Bare space 


50-0 
50-0 


0-3 
34-8 

64-9 


6-3 
30-5 

0-7 
62-5 


20 
19-2 

1-9 
76-9 




1000 


1000 


100-0 


100-0 



The aftermath on both sets of plots was grazed by cattle, and 
during the first week of October 1919 a determination of the ground 
space occupied by the various species was made, and the results are 
set out in Table XXIV. 

The clover had not reappeared at either centre in spite of the 
favourable chmatic conditions, and although the treated plots could 
be distinguished from the unmanured more than a mile away through- 



ON BOTANICAL COMPOSITION OF HERBAGE 



53 



out the whole winter and early spring, there was never any visible 
difference in the clover content between the treated and untreated 
plots. 

A chemical examination of the soils on the treated and untreated 
plots showed that at least one-half of the original dressing of phos- 
phoric acid was still present in an available form in the treated plots 
(see p, 105). The disappearance of the clover during 1919 was not 
therefore due to lack of phosphates. 

Table XXV. Botanical Composition of the Hay 
BY Weight at Martin's Hearne 
Sample taken: August 9th, 1920 





Plot 2 

Basic slag 

high soluble 

% 


Plots 

Untreated 

% 


Plot 4 
Gafsa rock 
phosphate 

/o 


Clovers 

Grasses 

Weeds 


27-5 

630 

9-5 


11-2 
58-5 
30-3 


350 
54-2 
10-8 



Table XXVI. Botanical Composition of the Hay 
BY Weight at Tysea Hill 

Sample taken: August 23rd, 1920 





Plotl 

Basic 

Bessemer slag 

/o 


Plot 2 

Gafsa 

phosphate 

/o 


Plot 3 

Untreated 

% 


Clovers 

Grasses 

Weeds 


5-9 

85-5 
8-6 


4-4 

89-6 

6-4 


4-4 

88-5 
71 



From March 1920 onwards the plots were inspected closely every 
week, and towards the end of May it became evident that the clover 
plant was again beginning to make headway, and by the end of July 
all the plots at Martin's Hearne, and particularly the rock phosphate 
plots, were covered with a vigorous growth of red and white clover. 
At Tysea Hill, less than half a mile away, there was very little clover 
showing, any difference there may have been between the treated 
and untreated plots in this respect was not discernible. Samples of 
hay from both centres were taken when the crops were cut, and the 
results of a partial botanical analysis are set out in Tables XXV 
and XXVI. 



54 



EFFECT OF PHOSPHATES 



A comparison of Tables XXV and XXVI brings out several points 
of considerable interest. In the first place the aU but complete dis- 
appearance of clover from the herbage at Martin's Hearne and Tysea 
Hill during the dry season of 1919, and the return of the clover at 
Martin's Hearne but not at Tysea Hill during the moist favourable 
season of 1920 is curious. Secondly, it will be noted that during the 
dry season of 1919 weeds formed about 30 % of the small crop on 
the imtreated plot at both centres. In 1920 weeds stiU formed about 
30 % of the crop by weight at Martin's Hearne, but at Tysea HiU 
the crop on the untreated plot was a heavy one and the hay on this 
plot was as free from weeds as on any of the treated plots. 

Table XXVII. Botanicax, Composition of the Hay by Weight 
AT Lambourne End (London Clay) 

Sample taken: July 17th, 1919. Manures sown: Jan. 4th, 1919 





Plot 2 

Basic slag 

high soluble 

% 


Plots 
No manure 

% 


Clovers, etc 

Grasses 

Weeds 


0-3 
88-7 
11-0 


00 

86-9 
13-1 




lOO-O 


1000 









Composition of the grasses by weight 



Cynosurus cristatus 


7-4 


6-3 


Avena flavescens 


4-3 


11-3 


Agrostis alba 


320 


36-9 


Holcus lanatus 


48-9 


34-2 


Anthoxanthum odoratum 


7-4 


11-2 



Lambourne End (London clay). The botanical composition of 
the hay at Lambourne End is shown in Table XXVII. As will 
be seen from this table, the phosphates were sown six months 
before the plots were cut. The season (1919) was a dry one, and the 
phosphates were without any appreciable effect on the clovers, which 
could therefore not act as an intermediary in encouraging th^ growth 
of the grasses. Nevertheless the basic slag plots jrielded almost twice 
the crop secured on the unmanured plot, a result which appears to 
indicate that phosphates have a direct and not an indirect action on 
the grasses, and that it is quite possible to obtain a specific and marked 
response to phosphates on pastures where clover plants are absent. 



ON BOTANICAL COMPOSITION OF HERBAGE 



55 



The moist season of 1920 was more favourable to the growth of 
clover, and during the latter part of May and the month of June 
the plots were rapidly covered with a luxurious growth of red and 
white clover. 

The botanical examination of the hay crop in 1920 is set out in 
Table XXVIII and is illustrated in Fig. 9. 

Table XXVIII. Botanical Composition op the Hay 
BY Weight at Lambouene End, 1920 

Sample taken: July 17th 





Plotl 

Open hearth 

(fluorspar) 

basic slag 

% 


Plot 2 

Open hearth 

high soluble 

basic slag 

% 


Plots 

No 

manure 

% 


Plot 4 

Egyptian 
phosphate 


Plot? 

Open hearth 

(fluorspar) 

basic slag 

Wigan 

% 


Plots 

Open hearth 

high soluble 

basic slag 

Wigan 

% 


Plot 9 

Cleveland 

phosphate 

% 


Clovers 
Grasses 
Weeds 


22-7 

67-8 

9-5 


25-6 
61-9 
12-5 


2-3* 
70-3 
27-4 


33-5 
59-3 

7-2 


15-2 
72-5 
12-3 


33-7 

57-9 

8-4 


38-6 
55-7 

5-7 




1000 


100-0 


100-0 


100-0 


100-0 


100-0 


1000 



* Practically all bird's foot trefoil, purple vetch and Vicia sativa. 



w 



n80 
70 _ 



60 . 



PM 



:rJH- 




FiG. 9. Botanical composition of the Hay, by weight, at Lambourne End. 
Season, 1920. Soil London clay. 

1, Open hearth (fluorspar) basic slag. 2, Open hearth (high soluble) basic slag. 
3. Untreated 4, Egyptian phosphate. 9, Cleveland phosphate. 

The results recorded in the above table simply afford another 
illustration of the effect of the various phosphates in encouraging the 
development of the clover plant. 

It would be difficult to secure poorer quahty hay than that obtained 
even on the slag plot in 1919. When conditions are favourable to the 
development of clover as was the case in 1920, phosphates, in addi- 
tion to an increased crop, produce a vastly better quahty of hay. 



56 



EFFECT OF PHOSPHATES 



Table XXIX. Botanical Composition of the Hay by Weight 

AT BUTTERFIELDS, LaTCHINGDON. SeASON, 1919 

Soil: London clay. Sample taken: July 21st. 
Manures sown: December, 1915 



Plotl 

Basic' 

Bessemer 

slag 

/o 



Plot 2 

Gafsa 

rock 

phosphate 

/o 



Plots 

No 

manure 

o/ 



Plot 4 

Open hearth 

(fluorspar) 

basic slag 

/o 



Plots 
Open hearth 
high soluble 
basic slag 1 

/o 



Plots 
Open hearth 
high soluble 
basic slag 2 

/o 



Clovers 
Grasses 
Weeds 



20-8 

74-4 

4-8 



15-8 

81-0 

3-2 



6-3 

87-9 
6-8 



17-6 

80-4 

20 



150 

82-8 
2-2 



18-0 

80-9 

11 



100-0 



100-0 



100-0 



100-0 



100-0 



Composition of the grasses by weight 



100-0 



Lolium perenne . . . 


14-4 


15-2 


10-8 


19-4 


241 


17-9 


Phleum pratense ... 


23-3 


21-3 


14-8 


190 


23-3 


25-6 


Cynosurus cristatus 


15-7 


18-3 


11-6 


20-4 


22-3 


19-3 


Poa trivialis 


8-5 


10-8 


7-6 


12-4 


15-7 


10-8 


Bromus mollis 


33-9 


8-7 


3-6 


4-2 


— 


— 


Hordeum pratense 


3-8 


21-8 


35-6 


19-6 


10-0 


15-5 


Agrostis alba 


— 


3-0 


6-8 


20 


2-0 


2-4 


Holcus lanatus ... 


0-4 


0-9 


8-3 


3-0 


20 


8-5 


A nthoxanthum 
odoratum 


— 


— 


0-9 


— 


0-6 


— 




100-0 


100-0 


100-0 


100-0 


100-0 


100-0 


Superior grasses ... 


61-9 


65-6 


44-8 


71-2 


85-4 


73-6 


Inferior grasses . . . 


381 


34-4 


55-2 


28-8 


14i6 


26-4 



rfloo 




Fig. 10. Botanical composition of the Hay, by weight, at Butterfields, Latchingdon. 
Season, 1919. Soil London clay. 
1, Basic Bessemer slag. 2, Gafsa phosphate. 3, No manure. 
4, Open hearth fluorspar basic slag. 5, Basic slag. 6, Basic slag. 



ON BOTANICAL COMPOSITION OF HERBAGE 



57 



Butterfields, Latchingdon. The effect of the various phosphates 
on the composition of the flora at Latchingdon is similar to that at 
Martin's Hearne and Tysea HiU. The botanical composition of the 
hay is shown in Table XXIX and in Fig. 10. The contrast between 
the treated and untreated plots is not so marked as at the other 
two centres mentioned, but the pasture on the untreated plot at 
Latchingdon is much superior to that at Martin's Hearne and Tysea 
Hill (compare Figs. 7, 8 and 10). On all the treated plots the better 
grasses, such as Lolium perenne, Phleum pratense, Cynosurus cris- 
tatus and Poa trivialis, have improved their position at the expense 
of the poorer quahty grasses, such as Hordeum pratense, Agrostis 
alba, Holcus lanatus, etc. It is worthy of note, moreover, that at 
Latchingdon clover forms a fair proportion of the crop by weight, 
whereas at Martin's Hearne and Tysea Hill it was practically absent 
during 1919. 



Table XXX. Botanical Composition op the Hay Crop 
BY Weight at Wendens, Saffron Walden. 

Soil: chalk. Sample taken: June 19th, 1919 
Manures sown: January, 1916 



Plotl 

Basic 

Bessemer 

slag 

/o 



Plot 2 

Gafsa 

rock 

phosphate 

/o 



Plots 

No 

manure 

% 



Plot 4 

Open hearth 

(fluorspar) 

basic slag 

% 



Plots 

Open hearth 

high soluble 

basic slag 1 

o/ 
/o 



Plot 6 

Open hearth 

high soluble 

basic slag 2 

% 



Clovers 

Grasses 
Weeds 



110 

86-9 

2-1 



101 

80-9 

9-0 



7-8 
82-2 
10-0 



8-2 

88-8 

30 



80 

84-5 

7-5 



6-9 

86-9 

6-2 



100-0 



100-0 



1000 



1000 



1000 



1000 



Composition of the grasses by weight 



Lolium perenne . . . 


64-4 


50-0 


45-4 


56-9 


43-4 


51-3 


Phleum pratense ... 


— 


— 


0-7 


— 


— 


— 


Dactylis glomerata 


3-7 


3-5 


3-8 


1-2 


8-0 


1-6 


Cynosurus cristatus 


8-6 


14-8 


14-6 


10-5 


11-9 


6-9 


Poa trivialis 


3-7 


4-0 


6-1 


3-6 


4-3 


5-9 


Avena flavescens ... 


5-8 


14-1 


13-9 


16-4 


13-5 


14-7 


Festuca ovina 


— 


— 


0-8 


— 


— 


— 


Holcus lanatus 


3-7 


1-3 


2-4 


2-7 


1-9 


2-6 


Bromus mollis 


10-1 


12-3 


12-3 


8-7 


170 


17-0 




100-0 


1000 


100-0 


1000 


100-0 


100-0 



58 



EFFECT OF PHOSPHATES 



Wendens, Saffron Walden. The botanical composition of the 
grass at Wendens, Saffron Walden (chalk) is shown in Table XXX. 
The quality of the meadow is obviously much superior to that at 
any of the other centres, and it is therefore not surprising to find 
that the various phosphates have had a comparatively small effect 
on the quahty of the herbage. 



Table XXXI. Botanical Analysis of the Hay Crop 
BY Weight at Horndon. 

Soil: London clay. Sample taken: Aug. 16th, 1920 
Manures sown: Feb. 27, 1918. Plots B, C, D and H: Feb. 3rd, 1919 



Plot 


Manure 


Clovers 


Grasses 


Weeds 


B 


Cambridge coprolites 


67-5 


28-7 


3-8 


C 


Lime 


20-6 


77-8 


1-6 


D 


Coarse ground open hearth (fluorspar) 










basic slag ... 


56-9 


38-1 


5-0 


1 


Florida pebble phosphate ... 


51-9 


40-0 


8-1 


3 


Algerian phosphate 


51-3 


45-8 


2-9 


5 


Open hearth basic slag (high citric soluble) 


45-4 


53-3 


1-3 


6 


Untreated ; 


8-7 


81-4 


9-9 


8 


Gafsa phosphate 


63-8 


320 


4-2 


9 


Tunisian „ 


47-7 


49-2 


31 


11 


Egyptian „ 


49-3 


47-7 


30 


13 


Superphosphate 


340 


61-4 


4-6 


15 


Superphosphate and Ume 


51-4 


47-9 


0-7 


16 


Untreated ... 


7-6 


85-5 


6-9 


17 


Open hearth basic slag (high citric soluble) 


441 


53-4 


0-5 


18 


Open hearth (fluorspar) basic slag (low 










citric soluble) 


45-5 


53-2 


1-3 


H 


Cleveland phosphate 


58-9 


38-5 


2-6 


K 


Untreated 


8-0 


80-1 


11-9 



Horndon (London clay). These plots were grazed during 1919, 
and samples of hay for botanical analysis were not removed until 
the 1920 crop was cut on August 16th. The results which are set out 
in Table XXXI, and iQustrated in Fig. 11, show an extraordinary 
contrast between the treated and untreated plots. In view of the 
effect of grazing during 1919 on the growth of the herbage on the 
plots receiving phosphates (see Table XV and Plates VI and VII), 
it is, however, not surprising to find that clover was the dominant 
constituent of the hay crop in 1920. 



ON BOTANICAL COMPOSITION OF HERBAGE 



59 



TOO 




B, Cambridge coprolites. C, Lime. 3, Algerian phosphate, 5. Open hearth (high 
soluble) basic slag. 6, Untreated. 8, Gafsa phosphate. 9, Tunisian phosphate. 



o 

a 



90 
80 
70 
60 
H50 
40 
30 
20 
10 



I" 



13 

L 



§15 

I 



^ 



16 



^HL 



[ 



^18 

L 



H 



^ 



11, Egyptian phosphate. 13, Superphosphate. 16, Super phosphate and lime. 16, Un- 
treated. 17, Open hearth (high soluble) basic slag. 18, Open hearth (fluorspar) 
basic slag. H, Cleveland phosphate. K, Untreated. 

Fig. 11. Botanical composition of the Hay, by weight, at Great Mulgraves, 
Horndon-on-the-HiU. Season, 1920. Soil London clay. 



DISCUSSION OF THE RESULTS OF THE 
BOTANICAL ANALYSIS 



Although a rapid and large increase in the amount of clovers 
present in the herbage has followed the application of phosphates 
at the various experimental centres, and although the various phos- 
phates appear to be equally effective in this respect, there are clear 
indications that the effect of the phosphates on the herbage is not 
confined to the clovers alone. At Martin's Hearne, Tysea HiU and 
Latchingdon for example (see Figs. 7, 8 and 10), the better types 
of grasses are greatly encouraged as a result of the apphcation of 
phosphates. The meadows at Martin's Hearne and Tysea Hill have 
been down for a considerable time. The nitrogen content and the 



60 



EFFECT OF PHOSPHATES 



organic matter content of the soil are already high, and it is difficult 
to beheve that the accumulation of a comparatively smaU amount 
of nitrogen by the nodule organisms and its subsequent nitrification 
is responsible for the double crop which the treated plots bore in 
1919 when no clover was present. It seems more probable that the 
double crop is due either to the grasses benefiting by the direct 
f ertihsing effect of the phosphates or to the phosphates having some 
action on the production of nitrates in the soil, or to the operation of 
both these causes. This contention is borne out by the results at 



Table XXXII. Botanical Composition op the Hay by Weight 
ON THE Plots receiving High Soluble Basic Slag. Season, 1919 





BoTTLDEB Clay 


London Clay 




Martin's 

Heame 

% 


Tysea 

HiU 

% 


Famham* 
% 


Lambourne 

End 

% 


Latching- 
don 
% 


Wendens 
% 


Horndon* 
% 


Clovers 

Grasses ... 
Weeds 


trace 
88-1 
11-9 


trace 
89-1 
10-9 


50-2 
33-3 
13-5 


0-3 

. 88-7 
110 


20-8 

74-4 
4-8 


110 

86-9 

21 


441 
28-6 
13-6 


Lime requirement 
RainfaUf (inches) 


0-27 
2-85 


0-29 
2-87 


0-00 
1-73 


0-45 
308 


003 
1-47 


000 
0-53 


0-00 
1-78 



* The figures for Farnham and Horndon indicate the percentage of ground space 
covered by the various species and not the botanical composition of the hay. It is 
obvious however that had a hay crop been cut at these centres clover woidd have 
formed a large proportion of the crop by weight. 

t May 1st till Harvest. 

Lambourne End, where a very large increased crop of grasses foUows 
the apphcation of phosphates, the response of the clovers to the 
dressing not being manifest until the following year (see Tables XXVII 
and XXVIII). 

Table XV clearly shows the superior effect of basic phosphates in 
encouraging the growth of clovers, but this effect once produced is 
not maintained on all the soils until the dressing of basic phosphates 
is exhausted or nearly so. 

At Horndon, Latchingdon, Saffron Walden and Famham no diffi- 
culty has been experienced in maintaining the clover even during a 
dry and unfavourable season like 1919. At Martin's Hearne, Tysea 
HiU and Lambourne End, however, the clover completely disappeared 
from the treated plots during 1919. This result at Martin's Hearne was 
rather surprising in view of the fact that clover covered the treated 
plots in 1918 almost to the exclusion of the grasses (see Plate IV). 



ON BOTANICAL COMPOSITION OF HERBAGE 



61 



These differences between the various centres are brought out 
clearly in Table XXXII. 

At Latchingdon and Wendens clover has persisted on the un- 
treated plots as far as can be ascertained ever since the fields went 
down to grass. There are, moreover, no signs of the clover which 
was encouraged by the apphcation of slag five years ago tending to 
'go off,' although, of course, it is subject to seasonal fluctuations. 

It wiU be noted that it is on the sour soils, and only the sour soils, 
that the clover failed during the season of 1919. 

If, however, the results for the 1920 season are tabulated, as is 
done in Table XXXIII, it wiU be seen that sourness is not the only 
factor. 

Table XXXIII. Botanical Composition of the Hay Crop by 

Weight on Plots receiving High Soluble Basic Slag. 

Season, 1920 





Maetin's Hearne 


TySBA HlIiL 


Lam- 

BOITENE 

End 

(average) 

2 plots 






Basic Slag plus 
slag alone lime* 

0/ 0/ 

/o /o 


Basic Slag plus 
slag alone lime* 

% % 


HOEN- 
DON 


Clovers 

Grasses 

Weeds 


27-5 

630 

9-5 


18-7 

73-3 

8-0 


5-9 

85-5 

8-6 


8-5 

84-9 

6-6 


29-7 
59-9 
10-4 


45-4 

53-3 

1-3 


Tiirae requirement 
Rainfall t (inches) 


0-27 
8-37 


— 


0-29 
9-34 


— 


0-45 
5-27 


0-00 
5-34 



* At the rate of 35 cwts. of CaO per acre. 



t May 1st tiU Harvest. 



On the sour soils at Lambourne End and Martin's Hearne clover 
forms more than 25 % of the crop, and it will be noted that a dressing 
of hme in addition to the slag has not improved the position of the 
clover at Martin's Hearne. It is, of course, quite possible that the 
clover on this plot will benefit by the dressing of lime should another 
unfavourable season succeed. 

The application of hme at Tysea Hill has not succeeded in bringing 
a vigorous growth of clover even in a favourable season hke 1920, 
and it is quite clear that some other factor besides chmate, hme and 
phosphate is responsible for the failure of the clover plant. 

Chemically the soil at Tysea Hill differs from that at Martin's 
Hearne in having a lower content of available potash, and it seems 



62 



EFFECT OF PHOSPHATES 



probable that an inadequacy of potash is responsible for the failure 
of the clover. 

The effect of grazing and continuous cutting on the condition of 
the botanical flora is well illustrated in Table XXXIV and Fig. 12, 
which show the percentage of the ground space covered by the flora 
on the slag plots at Latchingdon and Horndon during 1919. 

Table XXXIV. Percentage of the Ground Space occupied by 
THE Vegetation on the Basic Slag Plots 

AT Latchingdon and Horndon 
Determinations made: Aug. and Sept. 1919 





Latchingdon 

Cut 4 years in 
succession 


HOENDON 

Cut 1918 
grazed 1919 


Clovers 

Grasses 

Weeds ... 

Bare space 


181 

51-2 

00 

30-7 


45-2 

37-9 

7-5 

9-4 



cS 
ft 

13 



o 



PM 



60 



50 



40 



30 



20 



10 



i 



I 



n 



1 





Clover 

Crass 

Weeds 

Bare space 


x\\x\x 


iiiil 




Horndon. Cut 1918: 
grazed 1919. 



Latchingdon. Cut four 
years in succession. 

Fig. 12. Percentage of Ground Space occupied by the Vegetation on the Basic Slag 
Plots at Latchingdon and Horndon. Season, 1919. Soil London clay. 

The bottom at Latchingdon, it will be seen, is an open one, and 
although it shows a great improvement in this respect over the un* 
treated plot, it is not nearly so close as that at Horndon. At 
Latchingdon the clover disappears in the autumn and come again 
the following year towards the end of May or the beginning of June. 
At Horndon on the other hand the surface is covered with a network 
of clover runners, and there is practically no 'bare space' on the 
plot. The Essex farmer still holds to the practice of grazing and 
cutting his meadows in alternate years, and in view of these results 



ON MOISTURE CONTENT OF SOIL 63 

and the climatic conditions of the county, there is much to be said 
for this practice. 

The botanical analyses from all the centres agree in showing that 
as far as the quality of the herbage is concerned there is nothing to 
choose between the effectiveness of rock phosphates and high citric 
soluble basic slags. There are, however, indications that the open 
hearth (fluorspar) slags of very low solubiUty are less efficient in this 
respect than the high soluble basic slags. 

EFFECT OF PHOSPHATES ON THE MOISTURE CONTENT 
AND TEMPERATURE OF THE SOIL 

It has already been stated that one of the great difficulties experi- 
enced on the clay soils — particularly the London clay soils of Essex — 
is the wet condition under which they he throughout the winter and 
late spring. As a rule a hot and dry spell of weather succeeds, lasting 
during the greater part of May and June. The soil whether under 
pasture or arable conditions dries up rapidly, sets as hard as a brick 
(caps), and cracks badly. 

These unfavourable conditions were very obvious at the Horndon 
Experimental centre during 1919. Following a wet April the remains 
of a heavy faU of snow were still visible on the plots on May 3rd. 
A spell of dry hot weather set in and lasted without any recordable 
rain faUing until the third week in Jime. The condition of the un- 
treated plot was difficult to describe. There was practically no growth 
and the surface was covered with innumerable cracks, some of them 
wide enough to aUow of the insertion of the greater part of the arm. 
What Httle growth there was shrivelled up by the second week in 
June. It was obvious, however, that the plots receiving phosphates 
were not suffering nearly so badly. The cracks were fewer, and required 
looking for, and the thick matted bottom of clover provided a con- 
tinuous feed for the grazing stock throughout the season (Plate VI). 
The marked difference between the condition of the soil on the slag 
plot and untreated plot suggested a better regulation of the moisture 
supply on the former plot. 

It was Tuifortunately not possible during 1919 to follow up the 
enquiry which these observations suggested, but during the season 
of 1920 a series of moisture determinations and temperature records 
were made on Plot 17 (basic slag) and Plot 16 (untreated) at 
Horndon. 



64 



EFFECT OF PHOSPHATES 



MOISTITEE 

Commencing in March 1920 the moisture was determined each 
week in a 9 inches sample of soil from each plot, and a httle later 
3 inches samples were taken. At the same time temperature records 
were obtained at a depth of 9 inches and 3 inches. All the samples were 
taken by the writer and were secured by means of a 15 inches 
sampler of f inch diameter which could be adjusted to remove a 
core of 3 inches, 9 inches or 12 inches in length. The sample for each 
plot consisted of from 10-14 cores. 

Table XXXV. Moisttjre Content op the Soil at Horndon on 
Plots 16 and 17 at Various Depths 





Moisture (%) 


Date 


0-3 inches 


3-9 inches 




A 


* 




f • ■ -\ 




\ 




Plot 17 Plot 16 


Plot 17 


Plot 16 


1920 


Basic slag Untreated 


Basic slag 


Untreated 


April 26 


29-1 


28-6 


24-0 


29-6 


May 5 


26-1 


28-6 


22-8 


22-6 


10 


26-2 


29-3 


22-6 


25-0 


17 


22-8 


22-6 


17-8 


21-6 


25 


201 


18-4 


220 


21-5 


31 


23-7 


19-0 


15-4 


15-4 


June 8 


180 


15-9 


12-8 


151 


14 


19-5 


16-8 


15-6 


170 


21 


21-5 


19-9 


18-3 


181 


29 


18-7 


17-6 


13-4 


16-2 


July 8 


26-1 


25-8 


20-2 


23-8 


12 


26-3 


27-0 


24-3 


21-8 


20 


18-4 


18-4 


17-2 


19-1 


26 


23-2 


24-7 


210 


22-0 


Aug. 4 


24-2 


25-6 


19-6 


20-8 


9 


220 


24-9 


16-9 


191 


16 


18-8 


19-2 


15-5 


15-4 


31 


— 


190 


— 


17-8 


Sept. 7 


17-9 


18-7 


16-9 


17-2 


20 


26-8 


26-8 


23-2 


23-2 


Nov. 24 


25-3 


27-9 


191 


21-4 



The moisture contents of the first three inches of soil and of the soil 
from 3 inches to 9 inches on both plots are given in Table XXXV. The 
results are plotted together with the rainfall record in Figs. 13 and 14. 

Broadly speaking the 1920 season was a moist one, and particularly 
favourable for the hay crop. At the beginning of May the ground, 
as the result of a wet April, was saturated with water. May, however, 
was a dry, and on the whole a hot month, and the soil rapidly began 



ON MOISTURE CONTENT OF SOIL 



65 




26 3 IT 31 14- 28 12 26 B 23 6 20 27 
April May June July August Sept. 

Fig. 13. Moisture content of the first 3 inches of soil on the Untreated and Basic 

Slag Plots at Great Mulgraves, Homdon-on-the-Hill. Soil London clay. 
Plot 16, Untreated Plot 17, Basic Slag . Rainfall 




26 JO 24- 7 21 S 13 2 16 30 13 27 
April May June July August Sept. 

Fig. 14. Moisture content of the Soil at a depth of 3 to 9 inches on the Untreated 

and Basic Slag Plots at Great Mulgraves, Horndon-on-the-Hill. Soil London clay. 
Plot 16, Untreated . Plot 17, Basic Slag . Rainfall 

R.B.S. 5 



66 EFFECT OF PHOSPHATES 

to dry up. By May 25th the untreated plot had begun to crack and 
by June 7th it was difficult to find a square yard of this plot that 
was not traversed by a big crack. On this date also the first signs of 
'cracking' were observed on the slag plot, but the cracks required 
looking for and were of small dimensions. The dense growth on Plot 17 
was obviously taking much more water from the soil than was the 
case on Plot 16 where the growth was neghgible and where a large 
proportion of the surface was bare (see Table XV). The data presented 
in Table XXXV and Figs. 13 and 14, however, afford some explana- 
tion of these differences. On May 10th, Plot 16 (untreated) contained 
29 % of water, whilst Plot 17 contained approximately 26 %. By 
the 17th the moisture content of both plots had fallen to 23 %, 
Plot 16 having evidently lost its moisture at a more rapid rate than 
Plot 17. On the 25th the moisture content had fallen to 18-4 % on 
Plot 16, whilst Plot 17 in spite of the very much larger transpira- 
tion which was taking place from this plot contained 20-1 % of 
moisture, a difference of 1*7 % in favour of the slag plot. The week 
following the 25th was showery and hot, and on the 31st of May, 
when samples were again taken, there was a surprising difference 
between the moisture contents of the two plots to a depth of 3 inches. 
Plot 16 contained only 19 % of moisture, whilst Plot 17 had a 
moisture content of 23-7 %, a difference of 4-7 % in favour of the 
phosphate plot. Plot 16 received very httle benefit from the showers 
during the week ; much of the rain must have run down the cracks, 
and the bulk of the remainder, faUing on a bare surface exposed to 
the direct rays of the sun, was evaporated rapidly. The following eight 
days from May 31st to June 8th were dry and hot, no rain whatever 
falling. The moisture content of both plots fell rapidly, but on the 
8th, Plot 17, notwithstanding the much greater demand made upon 
it, contained 18 % of moisture in the first three inches of soil, com- 
pared with 15-9 % (the lowest moisture content recorded throughout 
the season) on the untreated plot. The advantage of a dense crop on 
this type of soil is fairly obvious, and it is in fact the only practical 
method of conserving the soil moisture. 

It is difficult to emphasise the importance of this indirect action 
of basic phosphates on this type of soil during a dry season when 
the absence of rainfall in May and June or a small precipitation 
makes the growth of a hay crop impossible. 

On the 10th of June the fine weather broke and during the sub- 
sequent fortnight unsettled conditions prevailed. Even at the end 
of a fortnight Plot 17, in spite of the rapid growth which was taking 



ON MOISTURE CONTENT OF SOIL 67 

place, still contained a higher moisture content in the surface 3 inches 
of soil than on Plot 16, where as far as the eye could judge the growth 
was all but neghgible. Apparently a good deal of the rain had drained 
down the cracks on Plot 16, which were stiU as prevalent as during 
the preceding fortnight. On July 1st a speU of wet weather set in, 
there being only two dry days during the first twelve days of the 
month. For this period a total of 1-97 inches of rain was recorded. 
On July 8th and 12th, when the samples were taken, both plots 
appeared to be equally wet and the cracks had all disappeared. The 
analytical results showed that on both these dates the surface three 
inches of soil on both plots had approximately the same moisture 
content. The third week of July was dry and growth on Plot 17 was 
rapid. At the end of the week both plots had the same moisture 
content, namely 18-4 %. The remaining week and the first week in 
August were wet and the moisture content of the surface three inches 
varied from 23-26 % ; the treated plot during the period 26th July 
to 9th August being distinctly drier. From the 9th of August to 
the 19th no rain fell, the untreated plot dried more rapidly and on 
the 16th the moisture content of both plots was approximately the 
same. On this date the plots were cut dead ripe; they were weighed 
on the 21st and carted to the stack and subsequently threshed foi 
wild white clover seed. The weights of hay on the two plots were, 
Plot 17, 28-8 cwts. and Plot 16, 6-4 cwts. per acre. 

It will be noted that from the 16th of August onwards (Plot 17 
no longer being covered by a dense crop) the moisture on both plots 
remained practically the same. 

By determining the moisture content of the soil to a depth of 
9 inches and 3 inches on both plots it was possible to calculate the 
moisture content of the layer of soil 3 inches to 9 inches on both plots. 
This was done, and the figures are given in Table XXXV, and are 
shown graphically in Fig. 14. The calculations were made with a view 
to ascertaining whether the crop on the basic slag plot was able to 
draw more water from the lower depth than was the case on the 
untreated plot. It is natural to expect this to be so under dry climatic 
conditions for either or both of two reasons. Firstly because of the 
increased root action which follows the application of basic phosphates 
to clay pastures, and secondly because it seemed possible that the 
remarkable root development which took place on Plot 17 would affect 
the texture of the soil to some extent and thereby facihtate the up- 
ward passage of capiUary water. An inspection of Fig. 14 shows that 
though the first three inches of soil on the basic slag plot remained 



68 EFFECT OF PHOSPHATES 

moister than on the untreated plot, throughout the dry periods, the 
opposite was the case as far as the moisture content of the 3rd to 
9th inch was concerned. Whenever a period of wet weather succeeded 
a dry spell, as for example during June 14th to 21st, the moisture 
content on both plots at a depth of 3-9 inches rose to approximately the 
same level. A dry spell invariably resulted in the moisture content of 
the 3rd to 9th inch on Plot 17 faUing more rapidly than on the un- 
treated plot. In view therefore of the high moisture contents which 
have prevailed at various periods throughout the season, it seems 
evident that the crop on Plot 17 has been able to utiHse the moisture 
at this depth, particularly during dry spells, to a much greater extent 
than was the case on the untreated plot. Mechanical analysis 
(admittedly imperfect for this purpose) fails to detect any difference 
in the mechanical structure of the soil on these two plots, and it is 
therefore probable that during the first years which follow the appH- 
cation of basic phosphate to this type of meadow land, the crop on 
the slag plot is able to draw upon the moisture content of the soil at 
lower depths than is the case on the untreated plot largely because of 
the increased root development. The behaviour of the two plots from 
August 16th, when the plots were cut, until September 20th^ tends 
to confirm this view. It will be seen that the moisture content of 
the section of the soU from 3-9 inches remained practically the same 
on both plots during this period and as far as the eye could judge 
no growth took place. 

Temperature 

The temperature records were taken by means of a special thermo- 
meter recording between 0° and 30° C, and graduated to one- tenth 
of a degree. During the latter stages of the work this thermometer 
was replaced by one registering only to one-fifth of a degree. It was, 
however, a simple matter to get results to one-tenth of a degree by 
interpolation. 

The temperature records of the soil on Plots 16 and 17 are given 
in Table XXXVI and are recorded graphically in Figs. 15 and 16. 
Examined in conjunction with the figures in Table XXXV (repre- 
sented in Figs. 13 and 14) the results have an important bearing 
upon the action of slag under dry cKmatic conditions on such heavy 
London clay soils. During the whole of the period from May 17th 
till the crop was carted off the plots on August 21st, the surface three 

1 Unfortunately the sample drawn from Plot 17 on August 31st met with an 
accident. 



ON THE TEMPERATURE OF THE SOIL 



69 



Table XXXVI. Temperature op the Soil at Horndon 
ON Plots 16 and 17, at Depths op 3 inches and 9 inches 





Temperature (degrees Centigrade) 


Date 


At a depth of 3 inches 
Plot 17 Plot 16 


At a depth 


of 9 inches 




Plot 17 


Plot 16 


1920 


Basic slag Untreated 


Basic slag 


Untreated 


May 5 


— 


— 


9-8 


10-3 


10 


— 


— 


— 


— 


17 


140 


160 


12-5 


13-5 


25 


17-2 


20-3 


14-7 


17-7 


31 


15-4 


21-4 


14-8 


16-2 


June 8 


14-4 


18-1 


13-5 


15-4 


14 


170 


200 


150 


18-0 


21 


16-3 


20-0 


15-8 


17-5 


29 


17-5 


20-5 


16-4 


19-2 


July 8 


15-3 


16-8 


14-8 


16-1 


12 


17-5 


19-8 


15-4 


17-9 


20 


16-5 


200 


15-6 


17-6 


26 


15-3 


16-3 


14-9 


16-2 


Aug. 4 


14-6 


17-6 


14-6 


16-2 


9 


15-2 


17-4 


14-9 


16-6 


16 


15-5 


19-2 


15-0 


16-8 


21 


130 


13-8 


— 


— 


31 


15-3 


14-7 


14-2 


13-9 


Sept. 7 


15-8 


15-5 


15-3 


14-8 


20 


12-2 


12-5 


12-6 


12-7 


Oct. 4 


13-4 


13-5 


13-6 


13-4 


Nov. 24 


4-5 


4-2 


5-2 


50 



o 23r 




n 24 7 21 S t9 Z 16 30 /4- Z8 5 
May June July August Sept. Oct. 

Fig. 15. Temperature of the Soil at a Depth of 3 inches on the Untreated and Basic 
Slag Plots at Great Mulgraves, Horndon-on-the-Hill. Soil London clay. 
Plot 16, Untreated Plot 17, Basic 



70 



EFFECT OF PHOSPHATES 



zor 




7 21 

June 



S /9 

July 



/6 30 /3 27 4 

August Sept. Oct. 

Fig. 16. Temperature of the Soil at a Depth of 9 inches on the Untreated and Basic 

Slag Plots at Great Mulgraves, Horndon-on-the-Hill. Soil London clay. 

Plot 16, Untreated Plot 17, Basic Slag . 

inches of soil on the slag plot remained considerably cooler than the 
surface soil on the untreated plot. The importance of securing an 
efficient covering of the surface soil, so as to protect it from the direct 
rays of the sun, is well brought out in Fig. 15. The thick bottom of 
clover has not only succeeded in retaining the moisture on Plot 17, 
but it has very effectively kept the plot cool during the hot spell 
of weather in May and June. A comparison of Figs. 13 and 15 shows 
quite clearly moreover that the lower temperature of the surface 
soil on Plot 17 is not due to the higher moisture which it contains, 
but is almost entirely due to the superior covering effect of the crop 
on this plot. 

During the hot period May 1 7th-25th the temperature of the surface 
soil on both plots rose considerably, and on the 25th there was a 
difference of 3-1° C. between them. The subsequent week was showery, 
a total of -24 inch falling on four of the seven days. Of this amount 
•14 inch feU on the 29th. On the 31st the temperature of Plot 17 
had fallen from 17-2° C. the previous week to 15-4°. Plot 16 on the 
other hand had risen from 20-3° on the 25th to 21-4° on the 31st 
there being now a difference of 6-0° C. between the two plots. In 
degrees Fahrenheit the temperatures at a depth of 3 inches on the 
two plots were— on Plot 16, 70-5° and on Plot 17, 59-7°. 

During the whole of May and June, Plot 17 (slag) at a depth of 
3 inches was never less than 3° C. cooler than the untreated plot. 
During the wet month of July the temperature on the two plots 
more closely approximated, but whenever a warm and dry speU of 



ON THE TEMPERATURE OF THE SOIL 71 

weather ensues the difference between the two plots becomes greatly- 
accentuated. On August 16th the plots were cut shortly after the 
temperature readings were taken, and the hay lay on the swathe 
until the 21st, when it was raked up, weighed and carted. The reason 
for the difference in temperature which had existed throughout the 
season soon became apparent. With the removal of the dense covering 
from Plot 17 the temperature records corresponded very closely with 
those of Plot 16, and in fact on several occasions were a trifle higher. 

The temperature records taken at a depth of 9 inches on each 
plot serve to emphasise the importance of an adequate covering of 
the soil. The beneficial effect of the covering action of the clover on 
the slag plot is very marked even at a depth of 9 inches, and during 
the warmest periods there is often a difference of 3° C. between the 
two plots. Plot 17 being invariably the cooler, despite the fact that 
the moisture content at this depth was generally lower than on Plot 16, 
the untreated plot. With the removal of the crop on August 21st 
this difference in the temperature records of the two plots at a depth 
of 9 inches becomes neghgible and the two curves follow each other 
very closely indeed. 

It is of course difficult to say how far this 'secondary effect' of 
the action of slag has contributed to the difference in the cropping 
power of the two soils (28-8 cwts. on Plot 17 and 6-4 cwts. on Plot 16), 
but there can be Httle doubt that it is of very considerable importance, 
and that during a dry season it may weU be the most important action. 

To retain moisture and keep the soil cool is the great difficulty 
experienced on this type of soil during the late spring and early 
summer. It is obvious therefore that whatever is possible should be 
done to maintain a thick close bottom, and for this purpose it is very 
desirable that the meadows should not be cut every year, but should 
be cut one year and grazed the next or two following years. To reserve 
a meadow for hay for several years is far from desirable under the 
climatic conditions prevaiUng in the east of the county, unless a hay 
crop varjdng from 1-7 cwts. of hay per acre should prove sufficiently 
profitable. 

Martin's Hearne. Itisof interest to compare the results at Horndon 
with those at Martin's Hearne. At Martin's Hearne the plots were 
cut for four years in succession and are known to have been cut for 
hay during the two years prior to the commencement of the experi- 
ments. There is no close bottom of clover at this centre such as that 
at Horndon (compare Tables XV and XXIV). At Martin's Hearne 
the clover dies down at the end of the season and in the following 



72 



EFFECT OF PHOSPHATES 



year makes its appearance towards the end of May if the season is 
a suitable one. During a dry unfavourable season Uke that of 1919 
clover was almost entirely absent (Table XXII). Moisture and tem- 
perature determinations were made on Plot 2 basic slag, and Plot 3 
untreated, throughout the season of 1920, and the records are shown 
in Table XXXVII. 



Table XXXVII. Effect of Basic Slag on the Moisture Content 

AND TeMPERATUEE OF THE SOIL AT MaRTIN's HbARNE 





Temperature (degrees Centigrade) 


Moisture 


Date 


Plot 2 


Plot 3 


Basic slag 


Basic slag 




Basic slag 


Untreated 


Plot 2 


Plot 3 


1920 


3 ins. 9 ins. 


3 ins. 1 9 ins. 


% 


/o 


Apr. 19 


1 








32-2 


35-1 


26 


— 


10-5 


— 


— 


341 


33-2 


May 5 


— 


9-9 


— 


9-7 


29-9 


31-6 


10 





— 


— 


— 


36-7 


34-6 


17 


— 


13-5 


— 


13-5 


25-3 


25-5 


25 


18-5 


15-9 


— 


— 


19-9 


21-3 


31 


16-9 


16-8 


16-8 


15-8 


27-9 


28-5 


June 8 


— 


— 


— 


— 


— 


— 


14 


17-6 


15-6 


18-1 


160 


23-3 


25-2 


21 


171 


16-8 


17-4 


16-8 


24-8 


23-4 


29 


17-8 


16-7 


17-8 


17-5 


16-7 


17-5 


July 8 


— 


— 


— 


— 


— 


— 


13 


170 


16-2 


17-3 


16-4 


25-6 


24-3 


19 


18-2 


15-8 


17-8 


16-4 


170 


18-3 


26 


14-7 


14-8 


14-6 


14-7 


25-1 


23-5 


Aug. 4 


14-9 


14-6 


14-9 


150 


26-8 


26-8 


9 


15-2 


14-6 


15-5 


14-8 


26-0 


23-6 


Plots cut 














Aug. 9th 














Aug. 16 


17-8 


16-4 


17-8 


16-4 


211 


20-2 


24 


15-7 


15-2 


15-6 


14-7 


22-8 


24-3 


31 


14-6 


140 


14-7 


14-3 


20-2 


18-6 


Sept. 7 


151 


151 


15-4 


15-3 


19-5 


200 


20 


14-8 


14-6 


14-8 


14-5 


25-3 


25-2 


Oct. 4 


140 


13-8 


14-1 


140 


— 


— 



At Martin's Hearne there is no appreciable difference in the tempera- 
ture records of the two plots either at a depth of 3 inches or at 9 inches. 
There is a big difference in the yield of hay on the two plots, namely, 
31-9 cwts. per acre on Plot 2, and 22-0 cwts. per acre on Plot 3. The 
bottom in both plots however is an open one, due to the recent 
practice of cutting every year, and the better growth on the slag plot 
does not act as a cover to any appreciable extent. 



ON TEXTURE OF THE SOIL 73 

The moisture figures also present no important point of difference. 
During the dry spells the slag plot, as might be expected considering 
the heavier crop which it carries, loses moisture at a more rapid rate 
than the untreated. 

The rainfall at Martin's Hearne and in the west of the county 
generally is considerably heavier than at Horndon-on-the-Hill, which 
is situated in the eastern part of the county. 

As a general rule it would be quite a safe practice in the west of 
the county to cut the meadows for hay every year, and Httle would 
be gained by alternating with grazing, except perhaps during a par- 
ticularly dry season hke 1919. 

THE EFFECT OF PHOSPHATES ON THE 
TEXTURE OF THE SOIL 

Collins (4), discussing the effect of phosphates on grass-land, states 
that on the untreated plot at Cockle Park yellow clay still remains 
close to the surface, yet on the plot which has been manured with 
basic slag for over twenty years a very useful loam extends to 10 or 
12 inches below the surface. The steady downward trend of the roots 
on the slag plot opens up the clay soil, and by admitting air and 
supplying organic matter gradually transforms the soil into a kindly 
loam. Such a transformation must of necessity have an important 
influence upon the movement of water in the soil. The experiments 
described here have only been running for a comparatively short 
time, and such an effect as Collins indicates would only be starting, 
and would not be readily noticed. The records of the moisture 
content at various depths on the two plots at Horndon (16 and 17), 
and the extraordinary contrast afforded by the root development, 
suggested that an appreciable alteration in the mechanical condition 
of the soil might have been brought about on the slag plot. In order 
to ascertain whether this difference is measurable by the ordinary 
methods of mechanical analysis, samples to a depth of 9 inches were 
removed from the slag and untreated plots at several of the centres 
during the autumn of 1919, and subjected to mechanical analysis. 
It cannot be said that the results, which are given in Table XXXVIII, 
afford much positive information. At Tysea Hill, Martin's Hearne 
and Butterfields, the clay fraction is appreciably less on the slag plots. 
At Farnham there is no difference, whilst at Horndon, where the 
experiment had only been iri progress for a year, the results are 
contradictory. In any case, the positive differences are so small as 
to be in each case within the limits of experimental error. 



74 



EFFECT OF PHOSPHATES 



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ON ACCUMULATION OF NITROGEN 



75 



It seemed probable in view of these results that three inch samples 
might show more clearly any alteration in the mechanical composi- 
tion which were in progress on the slag plots. Three inch samples 
were accordingly carefully removed from Plots 16, 17 and C at 
Horndon during August 1920 (two and a half years after the manures 
were sown), and submitted to mechanical analysis. The results are 
given in Table XXXIX. The differences between the figures for 
Plots 16 and 17 are smaller than the experimental error. 

It would seem therefore that the effects of basic slag on the moisture 
content of the soil which are described in the preceding section are 
not due to any improvement in the mechanical structiu-e of the soil 
that can be disclosed by the ordinary methods of mechanical analysis. 
This result must not of course be taken as indicating that the apphca- 
tion of basic phosphates to heavy clay pastures, and the consequent 
development of the clover, does not affect the mechanical condition 
of the soil, but simply that under the conditions of this particular 
experiment the differences in the behaviour of Plots 16 and 17 at 
Horndon with regard to moisture cannot be attributed to changes 
in the mechanical condition of the soil on the respective plots. 



Table XXXIX. Mechanical Analysis of the Soil at Horndon 

TO A DEPTH OF 3 INCHES 





Plot 17 


Plot 16 


PlotC 


Fraction 


Basic slag 

% 


Untreated 

% 


Lime 

% ■ 


Fine gravel) 

Coarse sand j 


203 


1-82 


2-27 


Fine sand ... 


10-30 


10-98 


13-33 


Coarse silt ... 


19-63 


18-61 


22-16 


Fine silt 


18-73 


18-62 


17-38 


Clay 


27-55 


27-74 


25-25 


Loss in solution 
,, on ignition J *"' 


Undetermined 


Undetermined 


Undetermined 









THE EFFECT OF PHOSPHATES ON THE ACCUMU- 
LATION OF NITROGEN IN GRASS-LAND 

Field experiments at Rothamsted, and later at numerous other 
places, have conclusively demonstrated that leguminous plants leave 
the soil richer in nitrogen in spite of the fact that they are highly 
nitrogenous themselves. Collins (4) has shown that the appHcation of 
phosphates, whether in the form of superphosphate or basic slag, on 



76 



EFFECT OF PHOSPHATES 



Tree Field, Cockle Park, has resulted in a considerable increase in 
the nitrogen content of the soil. In 1908 the percentage of nitrogen 
in the soil receiving phosphates was -236 %, whereas the untreated 
soil contained only -185 %. 

From analyses of the Tree Field soils in 1919 the results shown in 
Table XL were obtained. 

Table XL. Percentage op Nitrogen in the Soil 
OF Tree Field, Cockle Park 



Plot 




Nitrogen % 


4 
6 
8 


Basic slag 
Untreated 
Super and lime till 1905. 

Basic slag and lime 

1905-1919 


•249 

•172 

•228 



Analyses of the soil at the various Essex experimental centres after 
intervals of four, three and two years show that the gain in nitrogen 
on the plots receiving phosphates is considerable. The results are 
given in Table XLI. 



Table XLI. Percentage of Nitrogen in First 9 inches of Soil 





BoTTLDER Clay 


London Clay 


Chalk 




Martin's 
Hearne 
3 years 


Farnham 
3 years 


Butterfields, 

Latchingdon 

4 years 


Homdon 
2 years 


Wendens 
4 years 


Phosphate plots 
Untreated plot 


•338 
•299 


•231 

•208 


•260 
•248 


•234* 
•210t 


•244 
•219 



* Average of 8 plots. 



■ f Average of 2 plots. 



At Horndon samples were withdrawn from several of the plots in 
order to ascertain whether there was any difference in the influence 
of the various phosphates on the collection of nitrogen by the nodule 
organisms. The figures are set out in Table XLII. 

The samphng errors are probably considerable, and it would be 
unfair to argue too much from the comparison of one plot with 
another. If, however, the various rock phosphate plots are grouped 
together, the two basic slag plots, and the two untreated plots, more 
reUable data are obtained, as appears in the lower part of Table XLII. 



ON ACCUMULATION OF NITRATES 77 

The figures suffice to demonstrate that there is no difference between 
rock phosphates and basic slag so far as their effect on the collection 
of nitrogen is concerned, a conclusion which is borne out by the 
botanical analysis of the 1920 hay crop (Table XXXI, Fig. 11) and 
also by the botanical examination of the pasture in 1919 (Table XV, 
Plate VI). 

Table XLII. Percentage of Nitrogen 
IN Various Plots at Horndon 



Plot 




% nitrogen 


1 


Florida pebble phosphate 


! -240 


3 


Algerian phosphate 


•239 


5 


Basic slag 


•244 


6 


Untreated 


•212 


7^ 
8) 


Gafsa rock phosphate .. 


•227 


11 


Egyptian phosphate 


•247 


13 


Superphosphate 


•226 


15 


Superphosphate and lim( 


i ^222 


16 


Untreated 


•208 


17 


Basic slag 


•226 


erage 


of Rock phosphate plots .. 


•238 


„ 


two basic slag „ 


•235 




„ untreated „ 


•210 



THE RELATION OF PHOSPHATES TO THE ACCUMU- 
LATION OF NITRATES IN GRASS-LAND 

It has been suggested by Middleton(i5) that the secondary action 
of basic slag on pastures is due to the nitrification of the nitrogen 
accumulated by the nodule organisms, and that this resulting nitrate 
nitrogen is responsible for the vigorous growth of grasses which 
follows after the clover has been stimulated. 

In order to ascertain what effect the application of phosphates had 
on the production of nitrates in grass-land it was decided to make 
as far as possible weekly determinations of the nitrate nitrogen con- 
tent of the soil on the basic slag and untreated plots at three of the 
experimental centres. The centres selected were Martin's Hearne, 
where the soil has a hme requirement of -27 %, Lambourne End, a 
more sour type of soil with a hme requirement of -45 %, and Horndon- 
on-the-HiU, a 'sweet' soil containing a small reserve of calcium 
carbonate. 



78 EFFECT OF PHOSPHATES 

It was realised, however, that the experiment was complicated by 
the fact that the growing crops would probably remove nitrate as 
rapidly as it was formed, and that the much heavier crops on the 
slag plots would make a bigger demand on the nitrate supplies than 
would the crop on the untreated plots. 

To overcome this difficulty a supply of soil, taken to a depth of 
9 inches, from the slag and untreated plots at Martin's Hearne and 
Horndon-on-the-Hill was removed, transferred to Chelmsford, broken 
up, all the green growth removed, and then firmly packed into 10-inch 
glazed pots provided with a suitable drainage outlet. Particular care 
was taken to consohdate the soil in the pots by placing weights on 
the surface for some time and ultimately by tramping. The pots were 
placed in an open space under atmospheric conditions, and the nitrate 
nitrogen in the soil determined every fortnight. Samples for analysis 
were removed both from the field and from the pots by means of a 
small soil sampler similar to a cheese sampler. 

Estimation of the Nitrate Nitrogen. As soon as possible after 
the samples were taken — ^generally 4-5 hours in the case of the field 
soils and 30 minutes in the case of the pots — they were dried at a 
temperature of about 50° C. When dried the samples were finely 
ground and bottled. The nitrate nitrogen was estimated in the dry 
ground sample within four days of the sample being removed from 
the field. 

Method. From 50-100 gns. of soil were placed on a Biichner funnel 
and washed with several portions of distilled water until about 400- 
500 c.c. of filtrate were collected. The filtrate was transferred to a 
conical flask and then rapidly concentrated to a very small bulk — 
about 50-60 c.c. with 10 c.c. of normal caustic soda. The concentrated 
liquid so obtained was diluted with distUled water and boiled again 
for 10 minutes. The flask was cooled and 1 gram of finely powdered 
Devarda's alloy added. The contents were distilled into 10 c.c. of 
N/50 sulphuric acid, a specially prepared trap being used to prevent 
spitting. The burner was adjusted so that distillation proceeded 
slowly for about 5-10 minutes, at the end of which period distilla- 
tion was quickened so that about half the liquid passed over in 
30 minutes. Methyl red (-05 % solution in alcohol) was used as an 
indicator. 

The accumulation of Nitrate in the Pots. The soils representing 
Plots 2 and 3 at Martin's Hearne were potted on March 29th, and 
16 days later the first nitrate determinations were made. The soils 
from Plot 16 (untreated) and Plot 17 (basic slag) at Horndon were 



ON ACCUMULATION OF NITRATES 



79 



not removed and potted till April 19th, the first nitrate determination 
being made sixteen days afterwards on May 5th. 

The nitrate contents of the potted soils as determined at various 
dates throughout the season are given in Table XLIII. 

Table XLIII. Accumulation op Nitrate in the Potted Soils 
PROM Martin's Hearne and Horndon-on-the-Hill 



Date 



1920 



Martin's Hearne 
Boulder clay 



Basic 



Un- 
treated 



HORDON-ON-THE- 
HlLL 

London clay , 



Basic 



Un- 
treated 



Rain- 
fall in 
inches 



Mean 

max. 

temp. 

°C. 



Remarks 



Nitrate nitrogen parts per million of dry soil 



March 29 


0-96 


1-12 


— 


— 


— 


— 





April 


14 


6-16 


3-92 


— 


— 


1-89 


55-3 


Drains had run 




19 


— 


— 


2-24 


1-12 


— 


— 







21 


5-60 


3-50 


— 




1-00 


54-4 


Drains had run 


May 


5 


616 


3-04 


504 


1-68 


0-68 


66-0 


'9 99 




19 


9-52 


6-16 


5-60 


1-68 


0-24 


61-6 




June 


5 


12-88 


5-04 


9-52 


5-04 


2-10 


69-4 


Drains had run 




17 


17-04 


5-60 


12-88 


6-72 


0-22 


64-3 


— 


July 


2 


22-96 


7-28 


22-40 


7-00 


1-04 


68-8 


— 




14 


25-76 


7-84 


17-36 


6-84 


1-04 


63-3 


— 




29 


22-40 


7-54 


20-14 


504 


1-55 


69-6 


Drains had run 


Aug. 


11 


14-56 


8-40 


16-24 


5-60 


1-37 


67-7 


99 99 




25 


20-16 


18-48 


25-20 


4-48 


0-98 


71-6 




Sept. 


9 


19-36 


20-72 


28-00 


4-48 


0-21 


65-6 


, 




15 


23-52 


25-56 


— 


— 


0-13 


69-6 







27 


26-32 


10-64 


14-56 


7-84 


3-19 


68-8 


Drains had run 



The general trend of the figures for both centres is very similar. 
There is a rapid accumulation of nitrate on the slag plots during the 
period May 19th to July 2nd. The results are illustrated in Pigs. 17 
and 18. The curves indicate a much greater and a much more 
rapid accumulation of nitrate in the soil from the slag plots than in 
the soil from the corresponding untreated plots. This can only be due 
to one or both of two causes: 

1. The nitrification of the nitrogenous matter accumulated in the 
slag plots by the nodule organisms. 

2. The direct effect of the slag on the soil organisms which bring 
about nitrification. 

It is difficult to understand how the addition of a comparatively 
small amount of nitrogenous organic matter to the already big accu- 
mulation in the experimental soils can be responsible for such a 
difference. Particularly is this the case at Martin's Hearne where 



80 



EFFECT OF PHOSPHATES 



the untreated soil contain -299 % of nitrogen and 11-80 % of organic 
matter (loss on ignition). It seems far more probable, therefore, that 
the result is mainly due to the direct effect of the phosphates on the 
soil organisms bringing about nitrification. 




29 
March 



J2 2e IQ S4- 7 21 S /9 Z 16 30 /3 27 
April May June July August Sept. 

Fig. 17. Nitrate content of the Potted Soil from the Untreated Plot and the Basic 

Slag Plot, at Martki's Hearne. 8oil Boulder clay. Season 1920. Soil from 
Untreated Plot (3) Soil from Basic Slag Plot (2) . RainfaU 



za 


1 

cS 
u 




1 

y 




24 


- .«^ 




f 


\ 




s 


/\ 


/ 


\ 


20 


as 
60 


/ ^ 

/ 




\ 
\ 
\ 


/€ 


2 

- +3 


/ 


V 


\ 




^ 


1 






•s 


J 






12 




• 






a 


-1 

- « 




-^x^_.^^^^ 


^^ 


4 










•^ t y^ 








J — 1 — 1 I — 1 , 1 „ , 


1 1 1 1 


-.1. .._ r 1 



19 
April 



n 

May 



/4- 

June 



12 Z6 

July 



9 23 

August 



20 27 

Sept. 

Pro. 18. Nitrate content of the Potted Soil from the Untreated and the Basic Slag 

Plots at Great Mulgraves, Horndon-on-the-HiU. Soil London clay. Season 1920. 

Soil from Untreated Plot Soil from Basic Slag Plot . 

The difference between the slag and untreated plots is striking, 
and seems to indicate, in view of the fact that the Martin's Hearne 
soil is sour, that on both these tjrpes of soil a deficiency in phosphates 
is a more important factor in limiting nitrification than a deficiency 
in lime. 



ON ACCUMULATION OF NITRATES 81 

There is a slightly greater accumulation of nitrate in the pot 
representing the untreated soil at Martin's Hearne than in the corre- 
sponding pot for Horndon-on-the-Hill, which may be due to the fact 
that the former is a more open soil. On the other hand, it may be 
due to the fact that, although the soil at Martin's Hearne is sour, 
it has a considerably higher content of total and available phosphoric 
acid than the soil at Horndon. The figures are as follows : 

Martin's Heabnb Horndon-on-the-Hill 

0/ 0/ 

Total P2O5 -089 -078 

AvailaMe P2O5 -0046 -0030 

Lime requirement ... 0-27 « 0-00 

At no period throughout the season does the nitrate content of 
the untreated soil from Horndon ever approach that of the soil 
receiving basic slag. The two pots representing the treated and un- 
treated soils from Martin's Hearne behave somewhat differently. 
Until August 11th the figures are comparable with those representing 
the Horndon pots, but during the hot spell which succeeded, there is 
a rapid accumulation of nitrate in both the Martin's Hearne pots, 
and when sampled on August 25th and September 9th and 15th, 
the nitrate content of the slag and untreated pots was approxi- 
mately the same. The temperature during the period August 11th 
to September 15th was higher than at any other period during the 
season, and although the pot drains did not run, there was a sufficient 
precipitation to keep the soil moist. On August 18th-19th -88 inch 
of rain fell, and there was a fall of -10 inch on two consecutive days 
out of the remaining 13 days in August. Four out of the first five 
days in September were showery with a total precipitation of -21 
inch. There was no further rain until September 14th, when -13 inch 
fell. After the 15th September (which was the last date on which the 
nitrate content of the two pots was similar) until the 22nd the weather 
was wet, 3-19 inches of rain falling between the 15th and 22nd 
inclusive. The drains from both pots ran freely, but unfortunately 
the drainage water was not collected. From the 22nd to the 27th 
the weather was dry and hot, no rain falling, and on the 27th when 
the pots were sampled the slag pot contained 26' 32 parts per miUion 
of nitrate and the untreated pot 10-64 parts. The relative nitrate 
content of the two pots was therefore similar to what it had been 
up to August 11th. 

It is difficult to account for the curious results obtained during 
the period August 11th to September 15th. It may be that under 

R.B.S. 6 



82 



EFFECT OF PHOSPHATES 



the cKmatic conditions then prevailing the untreated soil at Martin's 
Hearne is capable of yielding sufficient phosphate to enable nitrifica- 
tion to take place at a much more rapid rate than at any other time 
during the season. 



8r3z 




Fig. 19. Nitrate content of the soil on the Untreated and the Basic Slag Plots at 

Great Mulgraves, Horndon. Soil London clay. Season 1920. 

Untreated Plot Basic Slag Plot . Moisture Content 



2-8 

?•«•- 

2-4- 

Z-2 - 

IS 
1-6 
I '4 
/■2 
1-0 

•8 
•6 
•4 
■2 



s. 



ft 

A ; \ 



>-*"t 



•y».«' I ♦«♦ ■ 



^•>^ ■ -—I" 



fS 


S 19 


3 


17 


3i 


/A za 


/£ Z6 


3 23 


March 


April 




May 




June 


July 


August 



6 20 

Sept 

Fig. 20. Rainfall at Great Mulgraves, Horndon. Season 1920. 

If, as is postulated here, it is correct, in view of these results, 
to assume that the main eJffect of phosphates on the production of 
nitrate in soils well stored with nitrogenous organic matter is due to 
their action on the nitrifying organisms, it is possible to explain the 
large increase in the hay crop obtained on the treated plots at 



ON ACCUMULATION OF NITRATES 



83 



Lambourne End in 1919. The various phosphates were not sown 
until January, 1919, and although clover was absent from aU the 
plots throughout the season, the treated plots gave almost twice 
the yield of the untreated. The result was not due to any stimulation 



_g 14 



a /2 



Z & 



4-, 



2Z S 19 S 17 31 J-^ 28 12 Ze S 23 ZO 
March April May June July Attguit Sept. 

Fig. 21. Nitrate content of the soil on the Untreated and Basic Slag Plots at Martin's 

Hearne. Soil Boulder clay. Season 1920. 

Untreated Plot . Basic Slag Plot . Moisture Content 



2 



2 8-; 



-36 


• 




.•• . 


.• .* • 




-32 . ,.** *V 


*• • * 




.• 


*• : 




8 •* 






-28 u •• 


• 




«•• 


< 


• 


or 




A ..••"-. 


-2* S 


*'. ; 


••..••. •• • • 


«4-l 


A 


•••**.• '• •• •* 


o 
-20 a 


A ' 


\/ A V ''-'' \J 




1 \ 


• / \ * 


o 

'"I 
•c 




A /a\ ^\ /A 




II 1 


1 1 1 1 1 1 1 f 



/4 


r32 J^"'»- 


*• ." 






c 


V \ 




/2 


-28 8 / 


• 






o. 


• ; '• J! 


-,••*• 


/O 


-24^ 


*. r \ : \ ?.. 








\ : '% : *. .* '•• 


•V **.. 


8 


-20^ 


i • : / 


'••••• 


6 
4- 
2 


■q 

= A. 

t t 1 


A 'A 

1 i 1 J 1 1 


1 1 1 1 1 



22 
Match 



S 13 Z 17 2i iA 28 /2 26 9 Z3 6 20 
April May June July Augasb Sept. 

Fig. 22. Nitrate content of the soil on the Untreated and Basic Slag Plots at Butcher's 

Farm, Lambourne End. Season 1920. Soil London Clay. 

Untreated Plot . Basic Slag . Moisture Content 

of the clover, and as the crop was composed entirely of grass and 
weeds, it seems probable that the much heavier crop on the treated 
plots was mainly due to the direct effect of the phosphates in stimu- 
lating the production of nitrates. 

6—^ 



84 



EFFECT OF PHOSPHATES 



Field Results. The nitrate figures for the samples of soil taken 
weekly from the slag and untreated plots at Horndon, Martin's 
Hearne, and Lambourne End are given in Table XLIVand the results 
are shown graphically in Figs. 19, 20, 21 and 22. 



Table XLIV. Nitrate Content of the Soils on the Basic Slag 
AND Untreated Plots during 1920 



Date 



Horndon 



Plot 16 
Untreated 



Plot 17 
Basic slag 



Lambourne End 



Plots 
Untreated 



Plot 2 
Basic slag 



Martin's Hearne 



Plots 
Untreated 



Plot 2 
Basic slag 



Parts per million of nitrogen as nitrate 



Mar. 15 


— 


— 


5-04 


2-8 


2-24 


2-80 


22 


2-8 


112 


2-24 


1-68 


1-12 


1-68 


29 


•56 


2-80 


2-24 


2-8 


1-12 


•96 


Apr. 12 


— 


— 


2-24 


1-12 


1-68 


•56 


19 


112 


2-24 


5-6 


1-68 


1-68 


1-68 


26 


2-24 


1-68 


1-68 


1-68 


2-24 


1-68 


May 5 


4-4 


5-6 


2-8 


3-36 


2-80 


8-40 


10 


S-36 


1-68 


SS6 


4-48 


5-04 


9-52 


17 


1-12 


2-24 


— 


— 


1-68 


2-24 


25 


2-24 


S-36 


112 


112 


112 


2-80 


SI 


2-24 


2-8 


112 


2-24 


112 


1-12 


June 8 


4-48 


12S2 


3-92 


616 


— 


— 


14 


2-24 


5-60 


2-24 


2-24 


2-80 


2-80 


21 


6-7 


S-64 


2-8 


3-36 


4-48 


5-04 


29 


SS6 


112 


1-68 


2-8 


1-68 


2-80 


Jtdy 5 


— 


— 


2-8 


4-48 


— 


— 


8 


2-24 


2-24 


— 


— 


— 


— 


12 


1-68 


3-36 


— 


— 


— 


— 


IS 





— 


1-68 


6-72 


5-60 


8-40 


19 


— 


— 


3-36 


1-68 


1-68 


5-04 


20 


SS6 


S-92 


— 


— 


— 


— 


26 


S-92 


2-24 


1-68 


2-24 


3-92 


1-68 


Aug. 4 


2-24 


5-60 


2-80 


504 


2-24 


4-48 


9 


2-8 


7-28 


1-68 


1-68 


S-S6 


5-04 


16 


2-8 


5-6 


— 


— 


2-8 


2-24 


21 


5-6 


S-36 


— 


— 


— 


— 


2S 


— 


— 


S-92 


5-92 


— 


— 


24 


— 


— 


— 


— 


3-36 


1-68 


SI 


S-92 


10-64 


S-92 


6-16 


5-6 


5^04 


Sept. 7 


7-28 


112 


1-12 


2-80 


6-72 


4-48 


20 


2-80 


1-68 


1-12 


1-68 


0-56 


112 



The curves at all three centres have a general similarity of appear- 
ance, and they demonstrate that at certain periods during the season 
there is a much greater accumulation of nitrate in the slag plots 
than in the untreated. 

Even on the very sour soil at Lambourne End nitrification seems 



ON ACCUMULATION OF NITRATES 85 

to be much more active in the slag plots than in the untreated. There 
is a distinctly greater accumulation of nitrate during the periods 
May 5th to 10th, May 31st to June 8th, July 5th to 17th, August 4th 
and August 23rd to September 7th. Reference to Fig. 19 shows that 
these periods roughly correspond to those periods at Horndon during 
which there is a much greater accumulation of nitrate in the slag 
plots, and with two exceptions, viz., May 31st to June 8th, and 
August 23rd to September 7th, these dates hold good for Martin's 
Hearne. On June 8th samples were not taken from Martin's Hearne, 
so this exception is easily accounted for. The figures for this centre 
for August 23rd to September 7th are curious. There is an accumula- 
tion on both the treated and untreated plots, but it is greater on the 
untreated than on the slag plot. Reference to Fig. 17 shows that 
the same result was obtained from the pots, and that at this period, 
and only at this period, did the nitrate in the untreated pot accumu- 
late to an extent at all comparable with the slag pot. This result in 
the field would seem to lend some weight to the suggestion that at 
this period of the season the soil on the untreated plot has been able 
to furnish sufiicient phosphoric acid to meet the requirements of those 
organisms engaged in the production of nitrates. 

These results are not in accordance with the conclusions come to 
by RusseU(25). As the result of his work on the "Nitrate Content of 
Arable Soils," he says: "that only in one year (1911) was there any 
evidence of the organisms responsible for nitrification being retarded 
by a deficiency of phosphates and potash." It must be noted, however, 
that the soil even on the untreated plot of Broadbaulk Field contains 
considerably more phosphoric acid (-114 %) than the soils at Horndon, 
Martin's Hearne, or Lambourne End. 

It is of interest to note that at Martin's Hearne and Lambourne 
End periods of high nitrate accumulation coincide as a rule with 
high moisture content of the soil, whilst at Horndon they coincide 
with periods of low moisture content. At Martin's Hearne and at 
Lambourne End the periods of high nitrate accumulation on the 
slag and untreated plots occur as a rule at the same time (Figs. 21 
and 22). 

At Horndon, on the other hand, periods of high nitrate accumula- 
tion on the untreated plot follow, about a week later, similar periods 
on the slag plot. This difference might possibly be due to some 
influence the crop may have on nitrate production, but RusseU(25), 
when investigating this subject, was unable to secure any definite 
data supporting such a contention. 



86 INFLUENCE OF PHOSPHATES 

It may be that an inadequate supply of available phosphoric acid 
on the untreated plot prevented the crop from utilising the accumu- 
lated nitrate when suitable conditions occur, and that the subsequent 
depressions in the nitrate content are due to rain washing the nitrate 
down to below the 9 inch level. 



THE INFLUENCE OF PHOSPHATES ON 
SOIL BACTERIA 

At the suggestion of Dr RusseU an attempt was made to ascertain 
what effect, if any, the apphcation of phosphates has had on the 
soil bacteria. PreUminary counts were made at Rothamsted during 
the autumn of 1919, but the results were contradictory. 

Phosphates are essential for the development of all types of 
bacteria. Fred and Hart (9) in an investigation on the comparative 
effect of phosphates and sulphates on soil bacteria show that phos- 
phates increase the number of soil bacteria, and they suggest that 
increased crop production of a soil resulting from the application of 
soluble phosphates is in part due to the promotion of bacterial 
activity. The work of Hoffman and Hammer (lO) demonstrates that 
phosphates greatly increase the amount of nitrogen fixed by Azoto- 
bacter and they came to the conclusion that for this purpose di- and 
tri-calcium phosphates are more effective than mono-calcium phos- 
phates. 

The soils at Martin's Hearne and Horndon are very deficient in 
phosphoric acid and if any positive results were to be obtained it 
seemed probable that it would be at these two centres. Samples for 
bacteriological examination were taken every month from March to 
August. The samples were secured by means of a small soil sampler 
which removed a 9 inch core of about | inch diameter. The sample 
from each plot consisted of four cores. Before use, the soil sampler 
was sterilised by means of a methylated spirit lamp, and the samples 
when drawn were placed in previously sterihsed bottles. 

The total counts for the treated and untreated plots at Martin's 
Hearne and Horndon are given in Table XLV. 

There is very Kttle difference between the bacterial counts repre- 
senting the two plots at Martin's Hearne, and apparently phosphate 
has had little effect in this direction. 

The two plots at Horndon show decided differences. During the 
months of May, June and July there are twice as many bacteria in 



ON SOIL BACTERIA 



87 



the slag plot as on the untreated, but in April and August the position 
of the two plots in this respect is reversed. 

Whenever possible during the season counts of the Azotobacter and 
nitrate organisms were made. The results are set out in Table XL VI. 

Table XLV. Bacterial Counts (in thousands) at Martin's 
Hearne and Horndon. (Agar-Albumose media) 





Mabtin's Heaene 


Horndon 


Date 


Plots 

Untreated 


Plot 2 
Basic slag 


Plot 16 
Untreated 


Plot 17 
Basic slag 


1920 
March 6 
29 
April 26 
May 25 
June 25 
July 20 
Aug. 17 


2935 
575 
1540 
6869 
6206 
5347 
7070 


4632 
1234 
1638 
3810 
6039 
4500 
7211 


5430 
8235 
5349 
4120 
8609 


2783 
19550 
9303 
8568 
4000 



Table XLVI. Counts op Azotobacter and Nitrate Organisms 

IN the Soil at Martin's Hearne and Horndon. 

(Thousands per grm.) 





Azotobacter 


Nitrate Organisms 


Date 


Martin's 


Hearne 


Horndon 


Martin's Hearne 


Horndon 




Plots 

Untreated 


Plot 2 
Basic slag 


Plot 16 
Untreated 


Plot 17 
Basic slag 


Plots 

Untreated 


Plot 2 
Basic slag 


Plot 16 
Untreated 


Plot 17 
Basic slag 


1920 
May 26 
June 21 
July 19 
Aug. 17 


4722 
2154 
1330 
3302 


4837 
1735 
1771 
4685 


1800 
1082 
1031 


7828 

3171 
4983 


149 


298 


483 

1600 
2680 


2903 

6401 
8411 



There are no important differences between the numbers of Azoto- 
bacter present on the treated and untreated plots at Martin's Hearne, 
but at Horndon these soil organisms have been considerably developed 
by the apphcation of phosphates. 

The numbers of nitrate producing organisms have been greatly 
increased on the basic slag plots at Horndon, a result which is in 
keeping with the much greater amounts of nitrate found in this 
soil throughout the season. (Tables XLIII and XLIV and Figs. 18 
and 19.) 



88 PHOSPHATES AND BACTERIA 

It is difficult to explain why at one centre the numbers of bacteria 
should show marked increases as the result of the application of 
basic slag, whilst at another centre, where the effect of the basic 
slag on the crop is quite as marked, the bacterial content does not 
appear to have been appreciably affected by the apphcation of basic 
slag. It may be that the lack of effect at Martin's Heame is due to 
the sourness of the soil, but counts made on the portion of the basic 
slag plot which had received a dressing of ground hme in April 1920 
showed no appreciable advantage in this respect over that portion 
of the plot which had not been so dressed. 



FACTOHS LIMITING THE YIELD OF HAY 

AND THE ACTION OF PHOSPHATES ON 

HEAVY CLAY SOILS 



THE EFFECT OF RAINFALL ON THE YIELD OF 
HAY FROM THE UNTREATED PLOTS 

I HE weight of the hay crop on the untreated plot at each of the 
experimental centres varies within very wide limits from year to 
year. When a dry season is experienced the crop is often a failure, 
whilst the same plot given a moister and more favourable season 
may reach the comparatively high production level of two tons to 
the acre. 

In Table XL VII the yield of hay on the untreated plots for the 
years 1916-20 is compared with the rainfall for the period May 1st 
till harvest at the corresponding rainfall stations. The results for 
four of the centres are shown graphically in Figs. 23 and 24. 

Table XL VII. Comparison of the Weights op Hay on the 

Untreated Plots and the Rainfall from May 1st till 

Harvest at the various Experimental Centres 



EXPEKIMENTAIi 

Centre 




1916 


1917 


1918 


1919 


1920 


Tysea Hill 


Hay cwts. per acre 
Rainfall in inches 


31-6 
5-94 


20-4 
5-36* 


17-7 

4-47 


11-6 

2-87 


38-3 
9-34 


Martin's Hearne 


Hay cwts. per acre 
Rainfall in inches 


— 


14-3 
6-27 


23-4 
11-51 


10-4 

2-85 


22-0 
8-37 


Lambourne End 


Hay cwts. per acre 
Rainfall in inches 





— 


— 


13-2 
308 


21-4 

6-27 


Hassobury 


Hay cwts. per acre 
Rainfall in inches 





11-1 

4-82 


23-4 
7-73 


10-9 
0-58 





Wendens, 
Saffron Walden 


Hay cwts. per acre 
Rainfall in inches 


51-2 
4-00 


25-4 

4-00 1 


33-4 

2-44 


14-3 
0-53 


250 

2-42$ 


Butterfields, 
Latchingdon 


Hay cwts. per acre 
Rainfall in inches § 


31-4 
3-41 


14-5 
2-32 


20-1 
2-51 


20-6 
1-47 


161 

2-28 



* -71 inch of rain fell three days before plots were cut. 
t 2-32 inches of rain fell on May 20th, 1917. 
j -57 inch of rain fell two days previous to cutting. 
§ Rainfall figures for period May 1st till June 30th. 



90 



EFFECT OF RAINFALL 



The figures for the centre at Wendens are perhaps the most striking, 
the hay crop on the untreated plot varying from 51 cwts. to 14 cwts. 
per acre. Similar, although not quite so marked, fluctuations occur 
at all the other centres. The yearly rainfall figures afford no adequate 
explanation of these differences. At Wendens, for example, the rain- 
fall for the year was 27-33 inches in 1917, and in 1918 when a bigger 
yield of hay was obtained, 25-68 inches. The distribution of the 
rainfall, however, seems to be of great importance, particularly during 




2 4 6 8 

Inches of Rainfall, May.l till Harvest 

Fig. 23. Influence of Rainfall on the Yield of Hay on the Untreated Plots at 
Tysea Hill # and Martin's Hearne O- 

the months of May and June. If the rainfall figures for the period 
May 1st till harvest are tabulated with the yield of hay on the un- 
treated plot, as is the case in Table XL VII, it wiU be seen that, with 
one or two exceptions which can be readily accounted for, there is 
a very close connection between the two sets of figiu-es. 

The rainfall figures have been taken from the records of the British 
Rainfall Organisation. Their station at Havering-atte-Bower is within 
two miles of each of the first three experimental centres. At Hasso- 
bury there is a rainfall station on the farm, whilst at Saffron Walden 



ON THE YIELD OF HAY 



91 



and Latchingdon the respective rainfall stations are within from two 
to four miles of the experimental centres. 

The curve representing the correlation of the hay yield with the 
rainfall at Saffron Walden is a very steep one, and shows quite 
distinctly that rainfall is the most important factor. 

At Tysea Hill and Martin's Hearne even a high rainfall from the 
1st of May till harvest of 9-34 inches and 11*51 inches respectively 




10 



12 



4 6 8 

Inches of Bainfall, May 1 till Harvest 
Fig. 24. Influence of Rainfall on the Yield of Hay on the Untreated Plots at 
" ~ -©, and Cockle Park ■ 



Wendens 



Butterfields 



produce crops of only 38-3 cwts. and 23-4 cwts. The manurial factor 
is clearly of greater importance at these two centres and particularly 
at Martin's Hearne. The curves are not nearly so steep as at Saffron 
Walden, and there is a much greater response to manuring. 

At Latchingdon the rainfall has more influence on the crop than 
at Martin's Hearne or Tysea Hill and less than at Saffron Walden. 
It was difficult to get any correlation between the rainfall and the 



92 EFFECT OF RAINFALL 

yield of hay on the untreated plot at this centre. Owing to a wet 
July in 1918 and 1920 the crops had to remain uncut during a spell 
of wet weather, which had little or no influence on the growth of 
the crop. In order to overcome this difficulty the rainfall figures 
from 1st May to June 30th have been taken for each year. One point 
in the curve falls far out of fine, namely that representing the rainfall 
and the hay yield for 1919. The reason for this divergence, however, 
is clear. After an exceptionally dry May and June, the first week 
of July was wet, -47 inch of rain falUng on the 2nd of the month 
and '29 inch on the 3rd. The crop was not cut till three weeks 
later, and during that time considerable growth was made, particu- 
larly by the clover plants. If the rain faUing on the first four days 
of July is taken into consideration the divergence of this particular 
point is rectified. 

In Fig. 24 the effect of rainfall on the yield of hay from the un- 
treated plot at Tree Field, Cockle Park, is shown, and the curve 
affords an interesting contrast to those representing the Essex centres. 
At Cockle Park rainfaU does not influence the yield of hay on the 
untreated plot, whilst in Essex rainfall at certain centres is the most 
important hmiting factor, and at all centres it has a great influence 
on the yield of hay. 



THE EFFECT OF RAINFALL ON THE YIELD OF HAY 
FROM THE PLOTS RECEIVING PHOSPHATES 

The field experiments recorded show that at all these centres the 
appHcation of phosphates results in a considerable increase in crop. 
The increase is least at Saffron Walden and greatesti at Horndon. 
The results at Tysea HiU indicate, however, that even poor as this 
soil is in phosphoric acid, the heavy dressing of 200 lbs. of phosphoric 
acid per acre is more than the soil requires over a period of five years, 
as equally good results accrue from the fighter dressing of 100 lbs. 
In Figs. 25 and 26 the increase resulting from the appHcation of phos- 
phates at each centre is correlated with the rainfall. It wiU be seen 
that at Latchingdon and Saffron Walden the increase in the hay 
crop on the phosphate plots steadily progresses with the rainfall, 
clearly demonstrating that rainfall is the controUing factor, and that 
with the limited rainfall at these centres little or no increase may be 
expected from other than phosphatic manures. At Tysea HiU and 
Martin's Hearne on the other hand the increase in the yield of hay 



ON THE YIELD OF HAY 



93 



due to phosphate varies within extremely narrow limits, and is not 
dependent upon the rainfall. The curve for Tysea Hill is a perfect 
limiting factor curve and indicates that some factor other than the 
rainfall and phosphates is limiting the yield of hay. The absence 
of any increase in yield due to phosphates in 1920 is curious. The 
season was a particularly favourable one, and owing to the rainy 
weather in July and the beginning of August the crop was not cut 
until August 23rd. As will be shown later, at least haK of the original 
dressing of phosphoric acid apphed in 1915 was stiU present in the 

16 
14 
12 
10 

8 

6 



12 3 4 5 

Inches of Rainfall, May 1 till Harvest 
Fig. 25. Influence of Rainfall on the Increase due to Phosphates at 
Wendens- # and Butterfields O. 

soil in an available form in October, 1919, so that the neghgible 
increase of the treated plots over the untreated in 1920 caimot be 
due to a deficiency in phosphates. It can only be concluded, therefore, 
that with a high rainfall (9-34 inches from May 1st till harvest) and 
a long growing period, no increase will be obtained from phosphates, 
unless the second hmiting manurial factor is first satisfied. The curve 
for Martin's Hearne closely resembles that at Tysea HiU, and as the 
two fields are on the same soil formation, have practically identical 
chemical and mechanical compositions, and are only a short 
distance apart ; the result at Martin's Hearne satisfactorily confirms 
the conclusion that a second hmiting factor comes into operation as 



s 








y 














9 


-1 




o 




J^ 




o 

1 






mt^ 


^ 




-s 




^ 


^ 


• 




1 


^ 


/ 


O 






c / 


/ 










/ / 












-/ / 












/ / 












^ 1 






1 1 


1 


J 



94 



EFFECT OF RAINFALL 



soon as the need for phosphates is satisfied. The soil at Martin's 
Hearne is appreciably poorer in total and available phosphoric acid 
than at Tysea Hill, and even with a rainf aU of 11 inches from May 1st 




i__J L_J L 



CD S 



I ' 



"d (u 

^■. ^ 

eg (B 

s w 

o 

m 

:^ 

O -TS 






1—1 02 



in 



CM 



o 



CO 



CO 



till hay harvest and a long growing period (cut August 10th), the 
soil cannot provide an adequate supply of phosphates. 

It is too soon to draw definite conclusions from the results at 
Lamboume End and Horndon-on-the-Hill. There are indications 



OTHER MANURIAL FACTORS 95 

that once the need for phosphates has been satisfied at Lambourne 
End the hay crop could be increased by the addition of some 
other essential plant food. It seems very probable, however, that 
at Horndon-on-the-Hill, after the need for phosphates has been 
satisfied, rainfall is the Umiting factor as far as the hay crop is 
concerned. 



THE SECOND LIMITING MANURIAL FACTOR 

It has been previously stated that the experiments were started 
with the object of ascertaining the relative manurial value of various 
types of insoluble phosphates. No attempt was therefore made to 
include dressings of potassic and nitrogenous manures. Out of the 
eight experimental centres dealt with here there are two — Hassobury 
and Farnham — at which the response to phosphates, measured by 
the hay crop, is negHgible. A very marked improvement in the 
quality of the meadow has resulted at Farnham, as has already been 
pointed out (Table XIII), but even in a favourable season the 
increased weight of hay resulting from the apphcation of the various 
phosphates has been very small indeed. Moreover, the productive 
level of this type of soil is exceedingly low, and the same remark 
apphes to Hassobury, where also the crop seldom passes the 10 cwts. 
per acre level. 

An examination of the analytical data presented in Table VII 
shows that the Hassobury soil is reasonably well supphed with phos- 
phoric acid, and has, in fact, practically twice as much available 
phosphoric acid as any of the other experimental soils. The percentage 
of available phosphoric acid is well above Dyer's limit of 0-01 %(7). 
This is not the case at Farnham, where the soil is markedly deficient 
in available phosphoric acid, and it seems reasonable to conclude 
that a deficiency of another essential plant food is the cause of the 
low productivity at Hassobury, and is preventing a response to the 
dressings of phosphates applied at Farnham. 

Both soils are weU suppHed with nitrogen, and as readily available 
nitrogen has been slowly accumulating at Farnham without having 
any appreciable effect on the hay yield, it does not seem that a lack 
of nitrogen is responsible for the poor crop returns. The Hassobury 
soil, though devoid of calcium carbonate and possessing a Hutchinson 
and MacLennan hme requirement of -13 %, gives no response to the 
heavy dressing of lime appHed to Plot 15. Moreover, the soil at 
Farnham has an adequate supply of calcium carbonate. The low 



96 OTHER MANURIAL FACTORS 

level of production at these two centres is clearly not due to soil 
sourness or lack of lime. 

Table XL VIII. Chemical Analysis of the Soils 
AT Hassobury and Farnham 



Hassobury Farnham 



Nitrogen 

Loss on ignition 
Calcium carbonate ... 
Total phosphoric acid 
Available „ „ 

Total potash 
Available potash ... 
Lime requirement . . . 



0/ 

/o 
0-180 


% 
0-208 


7-23 


8-23 


0-00 


0-45 


0-190 


0-118 


0-0123 


0-0056 


0-435 


0-644 


00194 


00165 



0-13 0-00 



The Hassobury soil has a lower content of 'total potash' than 
the other centres, but the Farnham soil is better off in this respect 
than several of the other centres. At both stations, however, the 
'available potash' is markedly lower than in any of the other clay 
soils, and although in both cases the figure is distinctly above Dyer's{7) 
limit, it seems difficult to come to any other conclusion than that a 
soil deficiency in available potash is responsible for the poor yields 
of hay at these two centres. 

At two of the remaining centres, namely Tysea Hill and Martin's 
Hearne, the curves in Fig. 26 show the operation of a second hmiting 
factor which comes into play after the need for phosphates has been 
satisfied. 

The soil at both these centres is very similar in composition. It 
is wen suppMed with organic matter and nitrogen, and as this store 
has been considerably added to by the accumulated residues from 
clover plants, it does not seem probable that there is any deficiency 
in nitrogen. 

Both soils are sour. They contain no calcium carbonate and have 
a high hme requirement. Nevertheless the production of nitrates in 
this soil compares very favourably with that at other centres better 
suppHed with calcium carbonate and where the soil is sweet. (Compare 
Figs. 21 and 19.) 

At Martin's Hearne and Tysea Hill the plots were cross dressed 
with hme at the rate of 35 cwts. per acre during the early part of 
1920, and at Martin's Hearne another plot was marked off and 
received a dressing of approximately 10 tons of farmyard manure 
to the acre. The results are recorded in Table XLIX. 



RESPONSE TO FARMYARD MANURE 



97 



There is a small gain due to lime at Martin's Hearne, but considering 
that the 1920 season was a particularly favourable one for the hay 
crop the result suggests that very httle can be expected from Hme 
imtil some other fertihsing constituent is supphed*. The same con- 
clusion holds true for Tysea Hill, where the increase due to Hme is 
insignificant. In taking the average it is probably not fair to include 

Table XLIX. Effect of Cross Dressing with Lime at Martin's 
Hearne and Tysea Hill 



Martin's Heaene 


Tysea Hill 




Hay cwts. 




Hay cwts. 


Plot 


per acre, 


1920 


Plot 


per acre, 

A 


1920 




UnUmed 


Limed 


Unlimed 


Limed 


1. Open hearth 






1. High grade basic 






(fluorspar) slag 


28-4 


28-5 


slag 


40-2 


40-1 


2, Ditto, high soluble 


31-9 


36-3 


2. Gafsa rock phos- 












phate 


41-2 


43.6 


3. Untreated 


230 


25-5 


3. Untreated 


38-3 


36-0 


4. Gafsa phosphate 


35-2 


39-6 


4. Open hearth 












(fluorspar) slag 


46-4 


49^9 


5. Egyptian phosphate 


29-0 


31-6 


5. Ditto, high soluble 


45-2 


47-2 


6. Algerian phosphate 


34-6 


34-7 


6. Ditto 


42-1 


41^6 


A. Farmyard manure 






7. Untreated 


45-6 


42^7 


(applied Autumn 


40-3 


38-7 


Half dressing of 






of 1919) 






phosphate 












8. Same as 2. 


48-3 


48^4 








9. Same as 6 


44-8 


430 








10. Same as 4 


44-8 


46^3 


Average 


31-8 


33-5 


Average 


43-7 


43^9 


Inches of rain. May 1st 
till harvest 


8-37 




9-34 


Lime requirement 


•27% 




•29% 



the results from the untreated plots, because it may with reason be 
argued that no result from the apphcation of Kme could be expected 
until the need for phosphates was first met. If the figures for the 
untreated plots at Tysea Hill are excluded, the average yield becomes 
44-1 cwts. per acre on the unhmed plots and 45-0 cwts. per acre on the 
hmed plots, giving an average increase of 0-9 cwt. in favour of Hme. 

The response to farmyard manure on Plot A at Martin's Hearne 
is significant. Assuming that 10 loads of farmyard manure are 
equivalent to 8 tons, and that the farmyard manure contained -4 % 
of phosphoric acid and -4 % of potash, this plot received in addition 

* The yields of hay for 1921 show equally poor returns from the use of lime. 



98 RESPONSE TO FARMYARD MANURE 

to other materials a dressing of phosphoric acid and potash equivalent 
to about 72 lbs. of each per acre. This amount of phosphoric acid 
was presumably sufficient to meet the requirements of the 1920 
season, and it is therefore interesting to note what effect the dressing 
of potash had^. 

There was no doubt throughout the whole season that the farm- 
yard manure plot was the best on the field. For the first time that 
portion of the field not within the experimental area, and which had 
received a similar dressing of dung, looked better and bore a better 
crop than the experimental plots. 

The average weight of hay on the phosphate plots was 31-8 cwts. 
per acre, and on the plot receiving a small dressing of phosphates 
and potash in the form of dung 40*3 cwts., leaving a gain of 8*5 cwts. 
per acre which can only be attributed to potash. 

During the whole season the plots were inspected once a week, 
and it was early evident that the clover was making a more vigorous 
growth on the farmyard manure plot. Owing to an oversight a 
sample of hay was not removed from this plot for botanical analysis. 

The aftermath was allowed to grow until the beginning of October, 
and not only was there a more vigorous growth, but the bottom of 
clover on the farmyard manure plot was closer and more regular 
than on any of the other plots. 

In view of the evidence there can be Httle doubt that on this 
type of soil, after the need for phosphate has been met, potash is the 
second hmiting manurial factor. Moreover it is very probable that 
in all but the exceptionally dry years a profitable return from the 
apphcation of potash will be secured. It should be possible by 
judicious apphcation of phosphates and potash to raise the produc- 
tion of meadow hay to the 2 tons an acre level in all but exceptionally 
dry years. 

Such results serve to confirm the conclusion that potash is the 
second hmiting manurial factor at Hassobury and Farnham, and 
they incidentally suggest that on grass-land in Essex profitable results 
from the apphcation of potash are hkely to accrue when the soil 
contains less than -03 % available potash — a figure considerably 
above Dyer's hmit. 

^ It is very improbable in view of the particularly moist season that the organic 
matter or the nitrogen in the farmyard manure plot had any effect on the yield of 
hay. The meadow has been down to grass for at least 80 years, and a large store of 
organic matter and nitrogen has been accumulated. The action of Hme would pre- 
sumably be to release these materials for the plant, and the lack of response to the 
apphcation of lime suggests that the soil can normally provide all the nitrogen the 
crop requires in a suitable form. 



THE ACTION OF BASIC SLAG ON THE 

ACIDITY OF THE SOIL AS MEASURED 

BY THE ' LIME REQUIREMENT ' AND 

HYDROGEN ION CONCENTRATES 

OF THE SOIL 

It is a matter of common knowledge that clovers, particularly 
wild white clover, are very sensitive to what is vaguely called soil 
acidity. The extent to which the clover plant is able to persist on 
a 'sour' soil probably depends, however, not only upon the degree 
of acidity as measured by the soil lime requirements, but upon such 
other factors as climatic conditions and the water holding capacity 
of the soil. 

On the Harpenden Common, Hutchinson and MacLennan^ found 
that wild white clover persisted where the soil had a lime requirement 
of -22 %, and they illustrate this by the following table. 

Table L. Relatioist of Lime Requirements of the Soil 
TO THE Vegetation on Harpenden Common 



Average lime require- 
ment of soil 


Dominant flora 


Approx. 0-22 % CaCOa 


Wild white clover 


„ 0-26 


Fescues 


„ 0-31 


Mixed; yarrow, woodrush and moss 


„ 0-39 


Gorse 


„ 0-43 


Yorkshire fog 


„ 0-53 


Sorrel 



The botanical analyses of the hay at the various Essex experi- 
mental centres shows that on poor heavy clay soils basic slag is able to 
induce a vigorous growth of clover even if the soil has as high a lime 
requirement as -45 %. The abiUty of the clovers to persist on such 
sour soils is, however, in Essex at any rate to a great extent dependent 
upon the distribution of the rainfaU. 

A comparison of Tables XXXII and XXXIII shows that during 
a moist growing season clovers form a large proportion of the hay 
crop on the basic slag plots, even when the soil has as high a lime 
requirement as -45 %. On a dry season, however, clovers are absent 

^ Journal of Agric. Science, vn. p. 102. 

7—2 



100 



LIME REQUIREMENT OF THE SOIL 



from the hay crops on all soils with a lime requirement between -13 
and -45 %, but are present on meadows which contain a small reserve 
of calcium carbonate, and whose hme requirement is neghgible. The 
absence of clover (which 'fills up the bottom') during a dry season 
adversely affects the yield of hay, and any factors which tend to 
produce conditions unfavourable to the clover plant obviously limit 
the yield. 

The acidity of the soil as measured by its 'hme requirement' does 
therefore to some extent hmit the action of basic slag, and it becomes 
of importance to ascertain to what extent the apphcation of basic 
slag affects favourably or unfavourably the acidity of the soil. 

Table LI. Lime Requirement and Ph. Value of the Soils 

IN THE Basic Slag and Untreated Soils at the Various 

Experimental Centres 





9 inches samples 


Ph. 


value 


3 inches samples 


Centre 


liime requirement 

, * ^ 

Basic slag Untreated 
% % 


Lime requirement 




Basic slag 


Untreated 


, * , 

Basic slag Untreated 
% % 


TyseaHiU 

Martin's Hearne 

Farnham 

Latchingdon 


•30 
•29 
•01 
•04 


•29 
•27 
•00 
•03 


6^2 
6-3 

7-4 
7-5 


6-2 

1-5 
7-6 


•35 
•03 


•31 

•04 
•13 



Samples of soil to a depth of nine inches and three inches were 
removed from the basic slag and untreated plots at several of the 
experimental centres during October 1919. The hme requirements of 
all the soils were ascertained and in some cases the Ph. value also. 
The results are set out in Table LI. 

In every case the hme requirement figures are higher for the soil 
on the basic slag plots than on the untreated, and although the 
differences are not great, they suggest that the apphcation of even 
a heavy dressing of basic slag is not sufficient to counteract the 
acidity which develops from the decaying organic matter which 
accumulates on such plots. The Ph. values also show but smaU 
differences, and with one exception, namely, the soils from Martin's 
Hearne, they confirm the hme requirement figures and indicate a 
tendency towards greater acidity on the basic slag plots. 

As it seemed probable that the continued use of basic slag over a 
long period of years would accentuate this tendency, samples of 
soil were secured from Plots 4, 6 and 8 at Tree Field, Cockle Park, 



LIME REQUIREMENT OF THE SOIL 



101 



through the courtesy of Professor Gilchrist, and the lime require- 
ment of the soil determined with the results given in Table LII. 

The acidity of the soil on Plot 4 is quite appreciably greater than 
on the untreated plot in spite of the fact that it has received, during 
the twenty-four years the experiment has been in progress, a total 
dressing of about two tons of basic slag to the acre. The botanical 
analyses of the hay from Plot 4 show moreover that it is not possible 
to maintain a permanent bottom of clover on this plot, and were it 
not for the comparison with Plot 8, it might reasonably be assumed 
that the sourness of the soil was responsible for the partial failure 
of the clover plant. Plot 8, however, has received a dressing of hme 

Table LII. Lime Requirement op Soil Samples for Plots 4, 6 
AND 8 AT Tree Field, Cockle Park 

Soil Samples taken 1919 



Plot 


Tkeatmbnt 

(Dressing of phosphate equivalent to 100 lbs. 

PgOg per acre) 


Lime 

requirement 

CaCO, 

/o 


CaCOg 

content of 

soil 

% 


4 

6 

8 


5 cwts. of basic slag every three years (1897-1919). 
Last dressing 1918 

Untreated 

Superphosphate + 10 cwts. ground lime every 
three years (1897-1905). 5cwts. basic slag+ 1 ton 
ground hme every three years (1905-1919). Last 
dressing 1918 


0-23 
0-20 

007 


0-00 
0-028 

0-29 



every three years since 1897, and since 1905 each application has 
been at the rate of 1 ton per acre, the plot receiving in the form of 
basic slag the same amount of phosphate as has been appHed to 
Plot 4. In all five tons of hme have been apphed to the plot, more 
than four times the amoimt required to satisfy the Hme requirement 
of Plot 4. There is now a small reserve of calcium carbonate in the 
soil on Plot 8, but in spite of this fact the soil has still a small 'hme 
requirement' and neither the crop nor the herbage are any better 
than on Plot 4. 

It seems fair to conclude from this evidence that the continued 
apphcation of heavy dressings of basic slag over intervals of three 
years does not suffice to supply the hme requirement of heavy clay 
soils imder grass. On the contrary the results indicate that such 
soils are hable to become even more sour than similar soil left 
untreated. 



102 LIME REQUIREMENT OF THE SOIL 

Although on sour clay soils basic slag fails to maintain a permanent 
plant of clover, yet the addition of heavy dressings of Hme fails to 
improve matters in this respect. At Cockle Park, a more vigorous 
growth of clover follows each successive dressing of slag, whilst in 
Essex on soils well supphed with calcium carbonate there is no 
difficulty in maintaining a permanent bottom of clover by the applica- 
tion of phosphates. (See results from Saffron Walden.) 

Why the Clover Plant Fails at Cockle Park 

The most important conditions necessary for the proper growth 
and development of the clover plant in conjunction with the various 
grasses are: 

1. A suitable supply of phosphate, 

2. A suitable supply of potash. 

3. The presence of calcium carbonate in the soil. 

4. Constant grazing to prevent the grasses shutting out the 
light and air, and thereby choking out the clover plant. 

At Cockle Park the plots have been grazed by sheep annually, so 
that the conditions in this respect are the most favourable possible 
for the permanent estabhshment of a bottom of clover. Potash in 
addition to basic slag on Plot 7 has not materially increased the 
returns, nor has it benefited the clover plant, and as has been indicated 
previously, no better results have attended the addition on Plot 8 
of ground Ume to the standard dressing of basic slag. 

A comparatively heavy dressing of phosphates (equivalent to 
100 lbs. P2O5 per acre) has been given to Plot 4 every three years 
and it would seem scarcely probable that a lack of phosphate was 
the cause of the wild white clover plant being unable permanently to 
estabHsh itself. Nevertheless, if the botanical composition of the 
herbage is examined over a period of years, it will be noted that 
following every dressing of basic slag there is a marked response by 
the clover plant. The results on Plot 8 apparently preclude any 
possibihty of the Ume in the basic slag being responsible for the 
improvement. By a process of ehmination one is forced to conclude 
that the various dressings of basic slag have never sufficed to meet 
the need for phosphates, and that at Cockle Park the level of produc- 
tion could be still further raised by increasing the dressing of phos- 
phoric acid or by repeating the present standard dressing at more 
frequent intervals. 

With the object of obtaining more precise information on this 



LIME REQUIREMENT OF THE SOIL 103 

point, the total phosphoric acid in the soils from Plots 4, 6 and 8 
was determined with the following results : 



Plot 4 



1919 

•088 % P2O5 
•052 
•076 



Plot 6 untreated at the beginning of the experiment contained 
•071 % of phosphoric acid. Plots 4 and 8 have each received 800 lbs. 
of phosphoric acid during the period of the experiment, sufficient, 
were there no losses, to raise the soil content of phosphoric acid to 
•107 %. Although the soil samples were removed less than two years 
after the previous dressing of basic slag had been suppUed, it will 



200 

180 

/60 
100 

80 
60 
40 
20 



O 



.g 




— K 



4- 5 

Year 



Tho. 27. Live Weight Gains on Basic Slag and Untreated Plots at Cockle Park. 
First Period, 1897-1905. Basic Slag Plot (3) . Untreated Plot (6) . 

be noted that the content of phosphoric acid in the soil on Plot 8 
is httle better than at the beginning of the experiment, and that the 
reserve of phosphoric acid in the soil from Plot 4 is much less than 
might have been anticipated. If the suggestion that phosphoric acid 
is still the Hmiting factor is correct, it would be natural to expect 
Plot 4 to give superior results to Plot 8. This is in fact the case(i3), 
and the inferiority of this latter plot over Plot 5 is not due to the 
depressing effect of hme on the hve weight gain, but to the fact that 
the soil on this particular plot contains a smaller supply of phosphoric 
acid than on Plot 4. 

If the increase in hve weight gain from Plot 3* over Plot 6. at Cockle 
Park during the period of the experiment is plotted out as is done in 
* Receives 200 lbs. of phosphoric acid as Basic Slag ev^ery six years. 



104 



LIME REQUIREMENT OF THE SOIL 



Eigs. 27 and 28, it will be seen that each successive application of 
basic slag results in a big increase in live weight gain during the two 
seasons following its apphcation. Thereafter the hve weight increases 
rapidly dechne until a fresh dressing is appHed, clearly indicating 
that during the third, fourth, fifth and sixth seasons following the 
apphcation of the heavier dressings of basic slag bigger returns could 
be obtained by a further dressing of phosphates. Gilchrist (i4) and 
SomerviUe(29) have pointed out that far from there being a falling 
off in the response to basic slag at Cockle Park, the hve weight gains 
are gradually increasing over each six year period. The improvement 
is slow, but it is due to the very slow building up of the phosphoric 
/80r 

^ f ^ 

• / ^v 



100 - 



o 



80- 



20 



7 7. 3 „ * sr 6 

Year 

Fig. 28. Live Weight Gains on Basic Slag and Untreated Plots at Cockle Park. 
Second Period, 1906-1911. Untreated Plot Basic Slag Plot . 

acid content of the soil. Such a result serves to confirm the conclusion 
that phosphoric acid is still the hmiting factor at Cockle Park, and 
that until the demand for phosphates is satisfied it will not be possible 
to estabhsh a permanent plant of clover and no improvement in the 
condition of the clover plant or in the live weight gains can be antici- 
pated by either the addition of Hme or of potash. 



Why the Clover Fails on some Pastures in Essex 

DURING THE DrY SeASON 

If the failure to secure a permanent bottom of clover on Tree Field 
at Cockle Park is due to an inadequate supply of phosphates in the 
soil, such is not the case at the experimental centres in Essex where 
this difficulty has been experienced. 

An inspection of Fig. 26 shows quite convincingly that at Martin's 
Hearne and Tysea Hill phosphoric acid is no longer a hmiting factor 



LIME REQUIREMENT OF THE SOIL 



105 



on the treated plots. A chemical analysis of the treated soils, more- 
over, reveals the fact that even after four years one-half of the 
original dressing of 200 lbs. of phosphoric acid is stiU to be found in 
the first nine inches of soil. Table LIII gives the total and available 
phosphoric acid found in the soil from the basic slag and untreated 
plots during the autumn of 1919. By assuming that one acre of soil 
to the depth of 9 inches weighs 1000 tons, the actual quantity of 
available phosphoric acid in the two plots has been calculated, and 
the excess in the basic slag plot taken to represent the amount of 
the original dressing still left in the soil. 

Table LIII. Total and Available Phosphoric Acid in the Soil 
FROM Basic Slag and Untreated Plots, in the Autumn oe 1919 



Samples taken 

Autumn of 

1919 


BUTTERBIELDS, 

Latchingdon. 

Manures sovm 

winter of 

1915-16 


Martin's 

Heabne. 

Manures sown 

winter of 

1916-17 


Tysea Hill. 
Manures sown 

winter 
of 

1915-16 


HORNDON. 

Manures sown 
Feb. 
1918 




Basic 

slag 


Un- 
treated 


Basic 
slag 


Un- 
treated 


Basic 
slag 


Un- 
treated 


Super, and 
lime, 15 


Un- 
treated, 16 


Total P2O5 ... 
Available PgOg 


% 

-088 
-0134 


0/ 
/o 

•077 
•0066 


% 

•101 
-0108 


0/ 
/o 

-089 
•0046 


/o 
•109 
-0102 


% 

-101 
•0051 


% 

-082 
-0106 


/o 

•078 
•0030 


Amoimt of 

PjOs added ... 
Amoimt found 

in citric acid 

solution 


lbs. 
200 

300-2 


lbs. 
147-8 


lbs. 
200 

241-9 


lbs. 
1030 


lbs. 
200 

228-5 


lbs. 
1142 


lbs. 
200 

237-4 


lbs. 
67^2 


Excess of avail- 
able phosphoric 
acid 


152-4 





138-9 




114-3 





170-2 






The above table shows that from a half to three-quarters of the 
original dressing of 200 lbs. of phosphoric acid still remains in the 
soil in an available form, and such results but confirm the conclusion 
that lack of phosphates can not be the cause of the clover faihng at 
Martin's Hearne and Tysea Hill during the dry season of 1919. 

The appHcation of hme at Tysea HiU and Martin's Hearne at the 
rate of 35 cwts. per acre of ground hme is more than sufficient to 
satisfy the hme requirements of these soils, and it would be reasonable 
to expect that if soil sourness is the only limiting factor to the 



106 



LIME REQUIREMENT OF THE SOIL 



growth of clover, a pronounced improvement in this respect will 
follow the appKcation of such a dressing. 

Throughout the whole of the 1920 season the plots were examined 
carefully every week. At Tysea Hill clovers were practically absent 
from the limed and unhmed portions of the plots, and it was quite 
obvious that some other factor than Hme and phosphates was pre- 
venting the development of clovers. 

At Martin's Hearne there was a good bottom of clover on all the 
plots although it was not so good as in 1918 (see Plate IV), and no 
improvement in this respect was evident on those portions receiving 
a dressing of Ume. 

Table LIV. Botanical Analysis of the Hay on Limed and 
Unlimed Plots at Tysea Hill and Martin's Hearne 

Tysea Hill 





Per cent, of Clovers in the Hay by weight 




Plotl 
Basic slag 


Plot 2 
Gafsa rock 
phosphate 


Plots 

Untreated 


Plot 7 
Untreated 


Plot 10 

Open hearth 

slag Ught dressing 


Unlimed portions 

of plot 
Limed portions 


5-9 

8-5 


4-4 
6-4 


4-4 
71 


0-8 
2-6 


3-8 





Martin's Hearne 






Per cent, of Clovers in the Hay by weight 




Plot 2 
Basic slag 


Plots 
Untreated 


Plot 4 

Gafsa 
phosphate 


Unlimed portions . . . 
Limed portions 


27-5 
18-7 


11-2* 

7-2* 


S50 
20-0 



* Mostly purple vetch and bird's-foot trefoil. Less than 3 % clovers. 

These observations were fully borne out by the botanical analysis 
of the hay at both centres on the unhmed and hmed portions of the 
various plots. The figures are given in Table LIV. 

Whether the appUcation of lime will enable the clovers to maintain 
their position at Martin's Hearne remains to be seen. If they fail in 
a dry season as was the case in 1919, then clearly some other essential, 
probably potash, is the factor limiting their growth. 

There can be little doubt that at Tysea HiU no further improve- 



LIME REQUIREMENT OF THE SOIL 107 

ment in the yield or quality of the hay can be secured without 
the application of potash, and that neither Ume nor phosphates nor a 
combination of the two will suffice to maintain a permanent bottom 
of clover. 

One other result calls for explanation. The superphosphate plot at 
Horndon, in spite of the fact that the soil contains a small reserve 
of calcium carbonate, has never held the same bottom of clover as 
any of the basic phosphate plots (see Plate VII and Fig. 11). Samples 
of soil were drawn in the autumn of 1919 from this plot, and from 
Plot 15, which received the same dressing of superphosphate (200 lbs. 
P2O5 per acre), and in addition 1 ton of lime per acre. On both samples 
the amount of citric soluble phosphoric acid and the Ume require- 
ment were determined, the results being as foUows: 

Plot 15 
Plot 13 Superphosphate 

Superphosphate and lime 



Total phosphoric acid 


•084 


% 

•082 


Available phosphoric acid 


•0046 


•0106 


Lime requirement 


•10 


•05 


Calcium carbonate 


•00 


•13 



The figures indicate that the inability of the clover to grow so 
vigorously on Plot 13 as on Plot 15 is not caused by sourness alone, 
but is mainly due to the phosphoric acid having been retained by 
the soil in a more unavailable form than is the case on Plot 15. 



REFERENCES 

(1) ARMSTRONG, S. F. The Botanical and Chemical Composition of the 
Herbage of Pastures and Meadows. J. Agric. Science, vol. ii, p. 283. 

(2) Baestbridge, R. The Effect of Fluorspar Additions on the Phosphates 

in Basic Slag. Iron and Steel Instit. Carnegie Schol. Memoirs. 1919. 

(3) BxjRiiisoN, W. L. The Availability of Mineral Phosphates for Plant 

Nutrition. J. Agric. Research, vol. vi. 

(4) Collins, S. H. Chemical Fertilisers. BalUere, Tindall, and Co. 

(5) Daubeny. On the Use of Spanish Phosphorite as a Manure. J. Boyal 
Agric. Soc. 1845. 

(6) DuTTON, F. V. Report on the Result of Field Experiments, 1912-14. Devon 
Cotmty Agric. Committee. 

(7) Dyer, B. Chemical Study of Phosphoric Acid and Potash in Wheat 
Soils of Broadbaulk Field, Rothamsted. Philosophical Trans. 1901, 
p. 235. 

Report on French Experiments. J. Royal Agric. Soc. 1896. 

(9) Fred, E. B. and Hart, E. B. The Comparative Effect of Phosphates 

and Sulphates on Soil Bacteria. Research Bulletin 35, Wisconsin. 
10) Hoffman, C. and HL^mmer, B. W. Some Factors Concerned in the 
Fixation of Nitrogen by Azotobacter. Research Bulletin 12, Wisconsin. 
LI) Hopkins, C. G. Soil Fertility and Permanent Agriculture. Ginn and Co. 
L2) Gilchrist, D. A. Guide to Cockle Park, 1915, pp. 39-43. 

[3) Ibid. 1914, pp. 11-15. 

L4) Best Methods of Laying Down and Improving Grass-land. 

J. Farmer's Club. 1920. 
MiDDLETON, T. H. The Improvement of Poor Pastiires. J. Agric. Science, 

vol. I, p. 134. 
Oldershaw, a. W. Yield of Grass from Variovis Basic Slags. J. Board 

of Agric. vol. xxiv, p. 819. 
Paterson, J. W. Utilisation of Phosphate Deposits in AustraUa. Bull. 7, 
Advisory Council of Science and Industry (Australia). 

(18) Robertson, G. S. A Comparison of the Effect of Various Types of Basic 

Slag on Grass -land. Trans. Faraday Soc. vol. xvi. 

(19) Influence of Fluorspar on the Solubility of Basic Slag in Citric 

Acid. J. Soc. Chem. Ind. vol. xxxv. 

(20) SolubiHty of Mineral Phosphates in Citric Acid. J. Soc. Chem. 

Ind. vols. XXXIII and xxxv. 

(21) Notes on the Nature of the Phosphates Contained in Mineral 

Phosphates. J. Agric. Science, vol. vni. 

(22) Reversion of Mixtures of Superphosphate. J. Soc. Chem. Ind. 

vol. XXXVI. 



REFERENCES 109 

(23) Russell, E. J. The Utilisation of Basic Slags. Trans. Faraday Soc. 

vol. XVI. 

(24) Notes on Manures, Jan. 1920. J. Ministry of Agric. vol. xxvi. 

(25) Nitrate Content of Arable Soils. J. Agric. Science, vol. vi. 

(26) Decomposition of Organic Matter in Soils. J. Agric. Science, 

vol. VIII. 

(27) SiLLARS, D. Formation of Basic Slag in the Manufacture of Steel. Trans. 

Faraday Soc. vol. xvi. 

(28) SoMEEViLLE, W. Manuring of Pastures for Meat and Milk. Ministry of 

Agric. Miscell. Pub. No. 30. 

(29) Grass. Presid. Address, Sec. M, Brit. Assoc. 1919. 

(30) Veeney, H. On the Spanish Phosphorite and other Manures. J. Roy. 

Agric. Soc. 1845. 

(31) Waggaman, W. H. and Wagneb, R. Agrictdtixral Availability of Raw 

Ground Phosphates. J. Ind. and Expt. Chem. vol. x. 

(32) Wood, T. B. and Berry, R. A. Soil Analysis as a Guide to Manuring. 

J. Agric. Science, vol. i. 



INDEX 



Agrostis alba, 32, 35, 36, 50, 51, 54, 56 

Algerian phosphate, 8, 21 

effect of, on accumulation of nitrogen 
in soil, 77; on the herbage, 35, 50, 
58 ; fine grinding on availability of, 32 
field trials with, 25 et seq. 

Alopecurus pratensis, 36 

Anthoxanthum odoratum, 50, 51, 54, 56 

Apatite, 11 

Armstrong, S. F., 36, 37 

Avena flavescens, 50, 51, 54, 57 

Azotobacter, 86 

Bacteria, influence of phosphates on soil, 

86 
Bainbridge, F., 10 
Basic slag 

comparison of, with superphosphate, 4 
effect of, on accumulation of nitrate 
in soU, 77 et seq. ; on accumulation 
of nitrogen in soil, 75; on bacterial 
content of soil, 86 et seq. ; on soil 
acidity, 99 et seq. ; on soil moisture 
content, 63 et seq.; on soil tem- 
perature, 68 et seq. ; on soil texture, 
73 et seq. 
grades available, 7 
high grade, 7 ; manufacture of, by open 

hearth process, 6 
production and consumption of, 5 
use on arable land, 4 
Basic Bessemer slag 

early experiments with, 3 

effect on botanical composition of 

herbage, 51, 52, 53, 57 
field experiments, 23, 27, 38, 44 
manufacture of, 2 
Basic open hearth slag 

comparison with Bessemer process, 5 
manufacture of, 4 
Basic open hearth slag (high sol.), 21 
effect on botanical composition of 

herbage, 28, 35, 39, 50 et seq. 
field experiments with, 23 et seq. 
Basic open hearth slag (fluorspar), 21 
effect on botanical composition of 

herbage, 28, 35, 39, 50 et seq. 
field experiments with, 23 et seq. 
manufacture of, 6 
pot experiments with, 10 
Belgian phosphate, 15 
Bellis perennis, 36 



Bones, 1 

dissolved, 2 
Boulder clay, soils, trials with various 

phosphates on, 22 et seq. 
Burhson, W. L., 11 
Butterfields. See Latchingdon 

Cambridge coprohtes, 21 

effect on botanical composition of 
herbage, 58, 59 

field experiments with, 31, 40 
Carolina phosphate, 8 
Centaurea nigra, 24 
Chalk soils, field experiments with various 

phosphates on, 43 
Cleveland phosphate, 21 

effect of, on botanical composition of 
herbage, 55, 58, 59 

field experiments with, 31, 40 
Clover, faUure of, 102, 104 
Cockle Park, 3, 4, 17, 24, 76, 100, 102 
CoUins, S. H., 8, 75, 78 
Coprohtes, 8, 15 
Cynosurus cristatus, 36, 50, 51, 54, 56, 57 

Dactylis glomerata, 36, 37 
Daubeny, Prof., 14 
Dundonald, Lord, 1 
Button, F. v., 10 
Dyer, B., 14, 96, 98 

Egyptian phosphate, 8, 21 

effect on accumulation of nitrogen in 
soil, 75 ; on botanical composition of 
herbage, 35, 50, 55, 58, 59; of fine 
grinding on availabflity of, 32 

field trials with, 25 et seq. 

Farnham Hall 

accumulation of nitrogen in soil at, 76 
effect of phosphates on the herbage at, 

29; on the soil texture at, 76 
field trials with various phosphates at, 

27 
limiting manurial factors at, 95 

Ferrous sulphate, influence of, on hay- 
crop, 31 

Festuca ovina, 50 

Field experiments, with various phos- 
phates, 18 et seq.; conclusions drawn 
from, 45 ; apphcabihty of the results of, 
48 



INDEX 



111 



Florida pebble phosphate, 8, 16, 21 
effect of, on. accumulation of nitrogen 
in the soil, 77; on herbage, 35; fine 
grinding on availability of, 33 
field experiments with, 27, 30 et seq. 
Florida soft phosphate, 21 

field experiments with, 31 
Fluorspar, 6 
Fred, E. B., 86 

Gafsa phosphate, 8, 16, 21 

effect of, on accumulation of nitrogen 
in soil, 77 ; on botanical composition 
of herbage, 28, 35, 50 et seq.; rain- 
fall on availability of, 44; soil acidity 
on availabihty of, 47 
field experiments with, 32 et seq. 
Gilchrist, D. A., 3, 15, 49, 101, 104 
Grazing and cutting, effect of, on com- 
position of herbage, 62 
Great Mulgraves. See Horndon 

Hammer, B. W., 86 
Hart, E. B., 86 
Hassobury 

field experiments with various phos- 
phates at, 26 
limiting manurial factors at, 95 
Hay 

effect of rainfall on yield of, 89 et seq. 
factors hmiting yield of, 89 et seq. 
yield of, at experimental centres, 18 et 
seq. 
Hoffman, C, 86 

Holcus lanatus, 50, 51, 54, 66, 57 
Hopkins, C. G., 11, 12 
Hordeum pratense, 36 
Horndon, 39, 40 

accumulation of nitrate in soil at, 77 et 

seq. ; of nitrogen in soil at, 76 
effect of grazing on herbage at, 62; of 
phosphates on bacterial content of 
soil at, 86; on herbage at, 35, 58; 
on soil moisture at, 63 ; on soil tem- 
perature at, 68; on soil texture, 73 
field experiments with various phos- 
phates at, 30 et seq. 
influence of rainfall on yield of hay at, 
89 et seq. 
Hutchinson, H. B., 99 
Hydrogen ion concentration, 26, 99 et 

seq. 
Hypochaeris radicata, 36 

Iron sulphate. See Ferrous sulphate 

Jamieson, 15 



Kirkman, I 

Lambourne End 

accumulation of nitrate in soil at, 77 
effect of phosphates on herbage at, 54 
field experiments with various phos- 
phates at, 39 
Latchingdon 

accumulation of nitrogen in soil at, 76 
effect of continuous cutting on herbage 
at, 62; of phosphates on herbage at, 
39, 59; on soil texture at, 73; of rain- 
fall on yield of hay at, 89 et seq. 
field experiments with various phos- 
phates at, 37 
Lawes, Sir John, 1 
Leontodon hispidus, 36 
Liebig, 1 
Lime 

effect on clover plant, 61, 105; on 
herbage, 58, 59, 61; on yield of hay, 
31,96 
Lime requirement, effect of basic slag on, 

of soU, 99 et seq. 
Lolium perenne, 36, 50, 51, 56, 57 
London clay, field experiments with 
various phosphates on, soils, 30 et seq. 

MacLennan, K., 99 
Martin's Hearne, 45 

accumulation of nitrates in the soil at, 

77 ; of nitrogen in the soil at, 76 
clover failure at, 96 
effect of lime on yield of hay at, 96; 
of phosphates on herbage at, 49, 59; 
on soil bacteria at, 86 ; on soil mois- 
ture at, 71; on soil temperature at, 
71; on soil texture at, 73; of rainfall 
on yield of hay at, 89 et seq. 
field experiments with various phos- 
phates at, 24 
Hmiting manurial factors at, 96 
Middleton, Sir T. H., 3, 49, 77 
Mineral phosphates. See Rock phos- 
phates 
Moisture, effect of phosphates on soil, 63 

Nitrates, estimation of, 78 

effect of phosphates on accumulation 
of, in soils, 77 et seq. 
Nitrogen 

effect of various phosphates on accu- 
mulation of, in soils, 75 
fixation by nodule organism, 49 

Ocean Island phosphate, 8 
Oldershaw, A. W., 15 



112 



INDEX 



Paterson, J. W., 17 

PfeifEer, 47 

Phleum pratense, 50, 51, 56, 57 

Phosphates 

action of, on heavy clay soils, 89 et seq. 
effect of, on accumulation of nitrates 
in soil, 77 et seq. ; on accumulation 
of nitrogen in soil, 75; on herbage, 
49 et seq.; on soil bacteria, 86; on 
soil moisture, 63 et seq. ; on soil tem- 
perature, 68 et seq. ; on soil texture, 
73 et seq. ; on yield of hay, 22 et seq. ; 
of fine grinding on availability of, 
32; of rainfall on availability of, 46; 
of sour soils on availability of, 47 

Poa trivialis, 50, 56, 57 

Potash, influence of, on yield of hay, 97 

Potentilla reptans, 36 

Prunella vulgaris, 36 

Rainfall, effect of, on availability of 
rock phosphates, 46; on perma- 
nency of clover, 60; on yield of hay, 
89 et seq. 
Ranunculus, 24, 36 
Rock phosphates 
Algerian, which see 
American, 8, 16 
composition of, 9, 21 
deposits of, 8 
Egyptian, which see 
field experiments with, in America, 11 ; 
in France, 14; in England, 14; in 
Scotland, 16; in Wales, 16; in Essex, 
18 et seq. 
Florida pebble, which see; soft, which 

see 
Gaf sa, which see 
Nauru, 8 

North African, 8, 33, 42, 48 
Ocean Island, 8 
Tunisian, which see 
Rothamsted, 75 
Mumex acetosa, 24 
RusseU, E. J., 16, 36, 85, 86 



Saussure, de, 1 

Sillars, D., 2, 6 

Soil 

analyses of, at experimental centres, 19 
bacteria, effect of phosphates on, 86 
moisture effect of phosphates on, 63 

et seq. 
som"ness, effect of phosphates on, 99 
sourness, effect of, on clover plant, 60 

61 
temperatm-e, effect of phosphates on, 

68 et seq. 
texture, effect of phosphates on, 73 

Somerville, W., 3, 104 

Spanish phosphorite, 1 

Stead, J., 40 

Stellaria media, 24 

Temperature, effect of phosphates on 

soil, 68 
Tree Field, 49 
Tunisian phosphates, 15, 21, 27 

effect of, on herbage, 35, 58, 59; of fine 

grinding on availability, of, 32 
field experiments with, 31, 40 
Tysea HUl Farm 

accumulation of nitrogen in soil at, 76 
effect of Ume on yield of hay at, 96; 
of phosphates on herbage at, 49 et 
seq.; on soil texture at, 72 et seq.; 
of rainfall on yield of hay at, 89 
failure of clover at, 104 
field experiments with various phos- 
phates at, 23 
limiting manurial factors at, 89 et seq. 

Verney, Sir H., Bart., 14 

Waggaman, 12 
Wendens 

accumulation of nitrogen in soil at, 76 
effect of phosphates on herbage at, 57, 
58; of rainfall on yield of hay at, 89 
field experiments with various phos- 
phates at, 43 



FEINTED IN ENGLAND BY J. B. PEACE, M.A. 
AT THE CAMBRIDGE TJNIVEESITY PEESS 



PLATE I 



113 




Poniing Slag and Metal from Basic Open Hearth Furnace. The molten slag 
is seen overflowing from the steel ladle into the slag ladle. 




Nauru Island. Shipping phosphate in bulk from Nauru Island. The phosphate 

has to be lightered off in surf-boats — over 1000 tons can be shipped in 9 hours. 

The steamer is lying in 150 fathoms of water. 



114 



PLATE II 




Ocean IslcDid Phospliate Workings. Coral pinnacles after most of the phosphate 
has been removed. A few feet more phosphate available below rail level. 




Ocean Island Phosphate Workings. Foreground: Most of the phosphate has 

been removed exposing the coral limestone pinnacles. Background : Phosphate 

deposit is intact and exists naostly in the form of gravel with occasional large 

boulders of phosphate rock. 

Coco-nut and other vegetation all growing in phosphate. 



PLATE III 



115 




Plot 1. Open Hearth Fluorspar Basic Slag. Martin's Hearne. June 3rd, 1918. 




Plot 2. Open Hearth High Citric Soluble Basic Slag. Martin's Hearne. 

June 3rd, 1918. 



116 



PLATE IV 




Plot 3. Untreated. Martin's Hearne. June 3rd, 1918. 




Plot 4. Gafsa Rock Phosphate. Martin's Hearne. June 3rd, 1918. 



PLATE V 



117 




Section of the Soil at Hassobury showing the presence^of chalk about 3 feet 

below the surface. (Photograph taken from the ditch at the bottom of 

the experimental field.) 



lis 



PLATE VI 




View looking down Untreated Plot K. Horndon. July 1920. 








View looking down Cleveland Phosphate Plot H. Horndon. July 1920. 



PLATE VII 



]19 





Basic Slag plot at Horndon. August 1919. 




Untreated plot at Horndon. August 1919. 



120 



PLATE VIII 




Gafsa Kock Phosphate plot at Horndon. August 1919. 




Photograph of chalk pit at Saffron Walden illustrating character of 
soil at Wendens' Experimental Centre. 



